author | Lennard de Rijk <ljvderijk@gmail.com> |
Mon, 13 Jul 2009 00:53:42 +0200 | |
changeset 2616 | 9321e100a7fb |
parent 109 | 620f9b141567 |
permissions | -rw-r--r-- |
109
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1 |
====================== |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
2 |
Database API reference |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
3 |
====================== |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
4 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
5 |
Once you've created your `data models`_, Django automatically gives you a |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
6 |
database-abstraction API that lets you create, retrieve, update and delete |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
7 |
objects. This document explains that API. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
8 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
9 |
.. _`data models`: ../model_api/ |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
10 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
11 |
Throughout this reference, we'll refer to the following models, which comprise |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
12 |
a weblog application:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
13 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
14 |
class Blog(models.Model): |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
15 |
name = models.CharField(maxlength=100) |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
16 |
tagline = models.TextField() |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
17 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
18 |
def __str__(self): |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
19 |
return self.name |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
20 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
21 |
class Author(models.Model): |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
22 |
name = models.CharField(maxlength=50) |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
23 |
email = models.URLField() |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
24 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
25 |
def __str__(self): |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
26 |
return self.name |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
27 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
28 |
class Entry(models.Model): |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
29 |
blog = models.ForeignKey(Blog) |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
30 |
headline = models.CharField(maxlength=255) |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
31 |
body_text = models.TextField() |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
32 |
pub_date = models.DateTimeField() |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
33 |
authors = models.ManyToManyField(Author) |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
34 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
35 |
def __str__(self): |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
36 |
return self.headline |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
37 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
38 |
Creating objects |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
39 |
================ |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
40 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
41 |
To represent database-table data in Python objects, Django uses an intuitive |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
42 |
system: A model class represents a database table, and an instance of that |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
43 |
class represents a particular record in the database table. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
44 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
45 |
To create an object, instantiate it using keyword arguments to the model class, |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
46 |
then call ``save()`` to save it to the database. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
47 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
48 |
You import the model class from wherever it lives on the Python path, as you |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
49 |
may expect. (We point this out here because previous Django versions required |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
50 |
funky model importing.) |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
51 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
52 |
Assuming models live in a file ``mysite/blog/models.py``, here's an example:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
53 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
54 |
from mysite.blog.models import Blog |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
55 |
b = Blog(name='Beatles Blog', tagline='All the latest Beatles news.') |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
56 |
b.save() |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
57 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
58 |
This performs an ``INSERT`` SQL statement behind the scenes. Django doesn't hit |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
59 |
the database until you explicitly call ``save()``. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
60 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
61 |
The ``save()`` method has no return value. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
62 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
63 |
To create an object and save it all in one step see the `create`__ method. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
64 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
65 |
__ `create(**kwargs)`_ |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
66 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
67 |
Auto-incrementing primary keys |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
68 |
------------------------------ |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
69 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
70 |
If a model has an ``AutoField`` -- an auto-incrementing primary key -- then |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
71 |
that auto-incremented value will be calculated and saved as an attribute on |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
72 |
your object the first time you call ``save()``. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
73 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
74 |
Example:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
75 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
76 |
b2 = Blog(name='Cheddar Talk', tagline='Thoughts on cheese.') |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
77 |
b2.id # Returns None, because b doesn't have an ID yet. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
78 |
b2.save() |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
79 |
b2.id # Returns the ID of your new object. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
80 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
81 |
There's no way to tell what the value of an ID will be before you call |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
82 |
``save()``, because that value is calculated by your database, not by Django. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
83 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
84 |
(For convenience, each model has an ``AutoField`` named ``id`` by default |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
85 |
unless you explicitly specify ``primary_key=True`` on a field. See the |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
86 |
`AutoField documentation`_.) |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
87 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
88 |
.. _AutoField documentation: ../model_api/#autofield |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
89 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
90 |
Explicitly specifying auto-primary-key values |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
91 |
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
92 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
93 |
If a model has an ``AutoField`` but you want to define a new object's ID |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
94 |
explicitly when saving, just define it explicitly before saving, rather than |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
95 |
relying on the auto-assignment of the ID. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
96 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
97 |
Example:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
98 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
99 |
b3 = Blog(id=3, name='Cheddar Talk', tagline='Thoughts on cheese.') |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
100 |
b3.id # Returns 3. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
101 |
b3.save() |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
102 |
b3.id # Returns 3. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
103 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
104 |
If you assign auto-primary-key values manually, make sure not to use an |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
105 |
already-existing primary-key value! If you create a new object with an explicit |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
106 |
primary-key value that already exists in the database, Django will assume |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
107 |
you're changing the existing record rather than creating a new one. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
108 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
109 |
Given the above ``'Cheddar Talk'`` blog example, this example would override |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
110 |
the previous record in the database:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
111 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
112 |
b4 = Blog(id=3, name='Not Cheddar', tagline='Anything but cheese.') |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
113 |
b4.save() # Overrides the previous blog with ID=3! |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
114 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
115 |
See _`How Django knows to UPDATE vs. INSERT`, below, for the reason this |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
116 |
happens. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
117 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
118 |
Explicitly specifying auto-primary-key values is mostly useful for bulk-saving |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
119 |
objects, when you're confident you won't have primary-key collision. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
120 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
121 |
Saving changes to objects |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
122 |
========================= |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
123 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
124 |
To save changes to an object that's already in the database, use ``save()``. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
125 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
126 |
Given a ``Blog`` instance ``b5`` that has already been saved to the database, |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
127 |
this example changes its name and updates its record in the database:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
128 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
129 |
b5.name = 'New name' |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
130 |
b5.save() |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
131 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
132 |
This performs an ``UPDATE`` SQL statement behind the scenes. Django doesn't hit |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
133 |
the database until you explicitly call ``save()``. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
134 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
135 |
The ``save()`` method has no return value. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
136 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
137 |
How Django knows to UPDATE vs. INSERT |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
138 |
------------------------------------- |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
139 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
140 |
You may have noticed Django database objects use the same ``save()`` method |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
141 |
for creating and changing objects. Django abstracts the need to use ``INSERT`` |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
142 |
or ``UPDATE`` SQL statements. Specifically, when you call ``save()``, Django |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
143 |
follows this algorithm: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
144 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
145 |
* If the object's primary key attribute is set to a value that evaluates to |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
146 |
``True`` (i.e., a value other than ``None`` or the empty string), Django |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
147 |
executes a ``SELECT`` query to determine whether a record with the given |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
148 |
primary key already exists. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
149 |
* If the record with the given primary key does already exist, Django |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
150 |
executes an ``UPDATE`` query. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
151 |
* If the object's primary key attribute is *not* set, or if it's set but a |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
152 |
record doesn't exist, Django executes an ``INSERT``. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
153 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
154 |
The one gotcha here is that you should be careful not to specify a primary-key |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
155 |
value explicitly when saving new objects, if you cannot guarantee the |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
156 |
primary-key value is unused. For more on this nuance, see |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
157 |
"Explicitly specifying auto-primary-key values" above. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
158 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
159 |
Retrieving objects |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
160 |
================== |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
161 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
162 |
To retrieve objects from your database, you construct a ``QuerySet`` via a |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
163 |
``Manager`` on your model class. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
164 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
165 |
A ``QuerySet`` represents a collection of objects from your database. It can |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
166 |
have zero, one or many *filters* -- criteria that narrow down the collection |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
167 |
based on given parameters. In SQL terms, a ``QuerySet`` equates to a ``SELECT`` |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
168 |
statement, and a filter is a limiting clause such as ``WHERE`` or ``LIMIT``. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
169 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
170 |
You get a ``QuerySet`` by using your model's ``Manager``. Each model has at |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
171 |
least one ``Manager``, and it's called ``objects`` by default. Access it |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
172 |
directly via the model class, like so:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
173 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
174 |
Blog.objects # <django.db.models.manager.Manager object at ...> |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
175 |
b = Blog(name='Foo', tagline='Bar') |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
176 |
b.objects # AttributeError: "Manager isn't accessible via Blog instances." |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
177 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
178 |
(``Managers`` are accessible only via model classes, rather than from model |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
179 |
instances, to enforce a separation between "table-level" operations and |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
180 |
"record-level" operations.) |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
181 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
182 |
The ``Manager`` is the main source of ``QuerySets`` for a model. It acts as a |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
183 |
"root" ``QuerySet`` that describes all objects in the model's database table. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
184 |
For example, ``Blog.objects`` is the initial ``QuerySet`` that contains all |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
185 |
``Blog`` objects in the database. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
186 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
187 |
Retrieving all objects |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
188 |
---------------------- |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
189 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
190 |
The simplest way to retrieve objects from a table is to get all of them. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
191 |
To do this, use the ``all()`` method on a ``Manager``. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
192 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
193 |
Example:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
194 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
195 |
all_entries = Entry.objects.all() |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
196 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
197 |
The ``all()`` method returns a ``QuerySet`` of all the objects in the database. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
198 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
199 |
(If ``Entry.objects`` is a ``QuerySet``, why can't we just do ``Entry.objects``? |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
200 |
That's because ``Entry.objects``, the root ``QuerySet``, is a special case |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
201 |
that cannot be evaluated. The ``all()`` method returns a ``QuerySet`` that |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
202 |
*can* be evaluated.) |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
203 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
204 |
Filtering objects |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
205 |
----------------- |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
206 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
207 |
The root ``QuerySet`` provided by the ``Manager`` describes all objects in the |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
208 |
database table. Usually, though, you'll need to select only a subset of the |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
209 |
complete set of objects. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
210 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
211 |
To create such a subset, you refine the initial ``QuerySet``, adding filter |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
212 |
conditions. The two most common ways to refine a ``QuerySet`` are: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
213 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
214 |
``filter(**kwargs)`` |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
215 |
Returns a new ``QuerySet`` containing objects that match the given lookup |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
216 |
parameters. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
217 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
218 |
``exclude(**kwargs)`` |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
219 |
Returns a new ``QuerySet`` containing objects that do *not* match the given |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
220 |
lookup parameters. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
221 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
222 |
The lookup parameters (``**kwargs`` in the above function definitions) should |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
223 |
be in the format described in `Field lookups`_ below. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
224 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
225 |
For example, to get a ``QuerySet`` of blog entries from the year 2006, use |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
226 |
``filter()`` like so:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
227 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
228 |
Entry.objects.filter(pub_date__year=2006) |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
229 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
230 |
(Note we don't have to add an ``all()`` -- ``Entry.objects.all().filter(...)``. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
231 |
That would still work, but you only need ``all()`` when you want all objects |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
232 |
from the root ``QuerySet``.) |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
233 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
234 |
Chaining filters |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
235 |
~~~~~~~~~~~~~~~~ |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
236 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
237 |
The result of refining a ``QuerySet`` is itself a ``QuerySet``, so it's |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
238 |
possible to chain refinements together. For example:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
239 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
240 |
Entry.objects.filter( |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
241 |
headline__startswith='What').exclude( |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
242 |
pub_date__gte=datetime.now()).filter( |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
243 |
pub_date__gte=datetime(2005, 1, 1)) |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
244 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
245 |
...takes the initial ``QuerySet`` of all entries in the database, adds a |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
246 |
filter, then an exclusion, then another filter. The final result is a |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
247 |
``QuerySet`` containing all entries with a headline that starts with "What", |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
248 |
that were published between January 1, 2005, and the current day. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
249 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
250 |
Filtered QuerySets are unique |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
251 |
----------------------------- |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
252 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
253 |
Each time you refine a ``QuerySet``, you get a brand-new ``QuerySet`` that is |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
254 |
in no way bound to the previous ``QuerySet``. Each refinement creates a |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
255 |
separate and distinct ``QuerySet`` that can be stored, used and reused. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
256 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
257 |
Example:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
258 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
259 |
q1 = Entry.objects.filter(headline__startswith="What") |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
260 |
q2 = q1.exclude(pub_date__gte=datetime.now()) |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
261 |
q3 = q1.filter(pub_date__gte=datetime.now()) |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
262 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
263 |
These three ``QuerySets`` are separate. The first is a base ``QuerySet`` |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
264 |
containing all entries that contain a headline starting with "What". The second |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
265 |
is a subset of the first, with an additional criteria that excludes records |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
266 |
whose ``pub_date`` is greater than now. The third is a subset of the first, |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
267 |
with an additional criteria that selects only the records whose ``pub_date`` is |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
268 |
greater than now. The initial ``QuerySet`` (``q1``) is unaffected by the |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
269 |
refinement process. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
270 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
271 |
QuerySets are lazy |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
272 |
------------------ |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
273 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
274 |
``QuerySets`` are lazy -- the act of creating a ``QuerySet`` doesn't involve |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
275 |
any database activity. You can stack filters together all day long, and Django |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
276 |
won't actually run the query until the ``QuerySet`` is *evaluated*. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
277 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
278 |
When QuerySets are evaluated |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
279 |
~~~~~~~~~~~~~~~~~~~~~~~~~~~~ |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
280 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
281 |
You can evaluate a ``QuerySet`` in the following ways: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
282 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
283 |
* **Iteration.** A ``QuerySet`` is iterable, and it executes its database |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
284 |
query the first time you iterate over it. For example, this will print |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
285 |
the headline of all entries in the database:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
286 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
287 |
for e in Entry.objects.all(): |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
288 |
print e.headline |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
289 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
290 |
* **Slicing.** As explained in `Limiting QuerySets`_ below, a ``QuerySet`` |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
291 |
can be sliced, using Python's array-slicing syntax. Usually slicing a |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
292 |
``QuerySet`` returns another (unevaluated )``QuerySet``, but Django will |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
293 |
execute the database query if you use the "step" parameter of slice |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
294 |
syntax. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
295 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
296 |
* **repr().** A ``QuerySet`` is evaluated when you call ``repr()`` on it. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
297 |
This is for convenience in the Python interactive interpreter, so you can |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
298 |
immediately see your results when using the API interactively. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
299 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
300 |
* **len().** A ``QuerySet`` is evaluated when you call ``len()`` on it. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
301 |
This, as you might expect, returns the length of the result list. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
302 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
303 |
Note: *Don't* use ``len()`` on ``QuerySet``\s if all you want to do is |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
304 |
determine the number of records in the set. It's much more efficient to |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
305 |
handle a count at the database level, using SQL's ``SELECT COUNT(*)``, |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
306 |
and Django provides a ``count()`` method for precisely this reason. See |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
307 |
``count()`` below. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
308 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
309 |
* **list().** Force evaluation of a ``QuerySet`` by calling ``list()`` on |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
310 |
it. For example:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
311 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
312 |
entry_list = list(Entry.objects.all()) |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
313 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
314 |
Be warned, though, that this could have a large memory overhead, because |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
315 |
Django will load each element of the list into memory. In contrast, |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
316 |
iterating over a ``QuerySet`` will take advantage of your database to |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
317 |
load data and instantiate objects only as you need them. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
318 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
319 |
Limiting QuerySets |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
320 |
------------------ |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
321 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
322 |
Use Python's array-slicing syntax to limit your ``QuerySet`` to a certain |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
323 |
number of results. This is the equivalent of SQL's ``LIMIT`` and ``OFFSET`` |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
324 |
clauses. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
325 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
326 |
For example, this returns the first 5 objects (``LIMIT 5``):: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
327 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
328 |
Entry.objects.all()[:5] |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
329 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
330 |
This returns the fifth through tenth objects (``OFFSET 5 LIMIT 5``):: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
331 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
332 |
Entry.objects.all()[5:10] |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
333 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
334 |
Generally, slicing a ``QuerySet`` returns a new ``QuerySet`` -- it doesn't |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
335 |
evaluate the query. An exception is if you use the "step" parameter of Python |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
336 |
slice syntax. For example, this would actually execute the query in order to |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
337 |
return a list of every *second* object of the first 10:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
338 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
339 |
Entry.objects.all()[:10:2] |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
340 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
341 |
To retrieve a *single* object rather than a list |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
342 |
(e.g. ``SELECT foo FROM bar LIMIT 1``), use a simple index instead of a |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
343 |
slice. For example, this returns the first ``Entry`` in the database, after |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
344 |
ordering entries alphabetically by headline:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
345 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
346 |
Entry.objects.order_by('headline')[0] |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
347 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
348 |
This is roughly equivalent to:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
349 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
350 |
Entry.objects.order_by('headline')[0:1].get() |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
351 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
352 |
Note, however, that the first of these will raise ``IndexError`` while the |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
353 |
second will raise ``DoesNotExist`` if no objects match the given criteria. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
354 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
355 |
QuerySet methods that return new QuerySets |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
356 |
------------------------------------------ |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
357 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
358 |
Django provides a range of ``QuerySet`` refinement methods that modify either |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
359 |
the types of results returned by the ``QuerySet`` or the way its SQL query is |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
360 |
executed. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
361 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
362 |
``filter(**kwargs)`` |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
363 |
~~~~~~~~~~~~~~~~~~~~ |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
364 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
365 |
Returns a new ``QuerySet`` containing objects that match the given lookup |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
366 |
parameters. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
367 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
368 |
The lookup parameters (``**kwargs``) should be in the format described in |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
369 |
`Field lookups`_ below. Multiple parameters are joined via ``AND`` in the |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
370 |
underlying SQL statement. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
371 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
372 |
``exclude(**kwargs)`` |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
373 |
~~~~~~~~~~~~~~~~~~~~~ |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
374 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
375 |
Returns a new ``QuerySet`` containing objects that do *not* match the given |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
376 |
lookup parameters. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
377 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
378 |
The lookup parameters (``**kwargs``) should be in the format described in |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
379 |
`Field lookups`_ below. Multiple parameters are joined via ``AND`` in the |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
380 |
underlying SQL statement, and the whole thing is enclosed in a ``NOT()``. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
381 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
382 |
This example excludes all entries whose ``pub_date`` is the current date/time |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
383 |
AND whose ``headline`` is "Hello":: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
384 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
385 |
Entry.objects.exclude(pub_date__gt=datetime.date(2005, 1, 3), headline='Hello') |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
386 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
387 |
In SQL terms, that evaluates to:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
388 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
389 |
SELECT ... |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
390 |
WHERE NOT (pub_date > '2005-1-3' AND headline = 'Hello') |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
391 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
392 |
This example excludes all entries whose ``pub_date`` is the current date/time |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
393 |
OR whose ``headline`` is "Hello":: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
394 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
395 |
Entry.objects.exclude(pub_date__gt=datetime.date(2005, 1, 3)).exclude(headline='Hello') |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
396 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
397 |
In SQL terms, that evaluates to:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
398 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
399 |
SELECT ... |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
400 |
WHERE NOT pub_date > '2005-1-3' |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
401 |
AND NOT headline = 'Hello' |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
402 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
403 |
Note the second example is more restrictive. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
404 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
405 |
``order_by(*fields)`` |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
406 |
~~~~~~~~~~~~~~~~~~~~~ |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
407 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
408 |
By default, results returned by a ``QuerySet`` are ordered by the ordering |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
409 |
tuple given by the ``ordering`` option in the model's ``Meta``. You can |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
410 |
override this on a per-``QuerySet`` basis by using the ``order_by`` method. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
411 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
412 |
Example:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
413 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
414 |
Entry.objects.filter(pub_date__year=2005).order_by('-pub_date', 'headline') |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
415 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
416 |
The result above will be ordered by ``pub_date`` descending, then by |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
417 |
``headline`` ascending. The negative sign in front of ``"-pub_date"`` indicates |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
418 |
*descending* order. Ascending order is implied. To order randomly, use ``"?"``, |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
419 |
like so:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
420 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
421 |
Entry.objects.order_by('?') |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
422 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
423 |
To order by a field in a different table, add the other table's name and a dot, |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
424 |
like so:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
425 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
426 |
Entry.objects.order_by('blogs_blog.name', 'headline') |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
427 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
428 |
There's no way to specify whether ordering should be case sensitive. With |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
429 |
respect to case-sensitivity, Django will order results however your database |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
430 |
backend normally orders them. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
431 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
432 |
``distinct()`` |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
433 |
~~~~~~~~~~~~~~ |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
434 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
435 |
Returns a new ``QuerySet`` that uses ``SELECT DISTINCT`` in its SQL query. This |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
436 |
eliminates duplicate rows from the query results. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
437 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
438 |
By default, a ``QuerySet`` will not eliminate duplicate rows. In practice, this |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
439 |
is rarely a problem, because simple queries such as ``Blog.objects.all()`` |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
440 |
don't introduce the possibility of duplicate result rows. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
441 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
442 |
However, if your query spans multiple tables, it's possible to get duplicate |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
443 |
results when a ``QuerySet`` is evaluated. That's when you'd use ``distinct()``. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
444 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
445 |
``values(*fields)`` |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
446 |
~~~~~~~~~~~~~~~~~~~ |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
447 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
448 |
Returns a ``ValuesQuerySet`` -- a ``QuerySet`` that evaluates to a list of |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
449 |
dictionaries instead of model-instance objects. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
450 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
451 |
Each of those dictionaries represents an object, with the keys corresponding to |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
452 |
the attribute names of model objects. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
453 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
454 |
This example compares the dictionaries of ``values()`` with the normal model |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
455 |
objects:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
456 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
457 |
# This list contains a Blog object. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
458 |
>>> Blog.objects.filter(name__startswith='Beatles') |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
459 |
[Beatles Blog] |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
460 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
461 |
# This list contains a dictionary. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
462 |
>>> Blog.objects.filter(name__startswith='Beatles').values() |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
463 |
[{'id': 1, 'name': 'Beatles Blog', 'tagline': 'All the latest Beatles news.'}] |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
464 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
465 |
``values()`` takes optional positional arguments, ``*fields``, which specify |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
466 |
field names to which the ``SELECT`` should be limited. If you specify the |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
467 |
fields, each dictionary will contain only the field keys/values for the fields |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
468 |
you specify. If you don't specify the fields, each dictionary will contain a |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
469 |
key and value for every field in the database table. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
470 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
471 |
Example:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
472 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
473 |
>>> Blog.objects.values() |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
474 |
[{'id': 1, 'name': 'Beatles Blog', 'tagline': 'All the latest Beatles news.'}], |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
475 |
>>> Blog.objects.values('id', 'name') |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
476 |
[{'id': 1, 'name': 'Beatles Blog'}] |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
477 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
478 |
A ``ValuesQuerySet`` is useful when you know you're only going to need values |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
479 |
from a small number of the available fields and you won't need the |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
480 |
functionality of a model instance object. It's more efficient to select only |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
481 |
the fields you need to use. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
482 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
483 |
Finally, note a ``ValuesQuerySet`` is a subclass of ``QuerySet``, so it has all |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
484 |
methods of ``QuerySet``. You can call ``filter()`` on it, or ``order_by()``, or |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
485 |
whatever. Yes, that means these two calls are identical:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
486 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
487 |
Blog.objects.values().order_by('id') |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
488 |
Blog.objects.order_by('id').values() |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
489 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
490 |
The people who made Django prefer to put all the SQL-affecting methods first, |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
491 |
followed (optionally) by any output-affecting methods (such as ``values()``), |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
492 |
but it doesn't really matter. This is your chance to really flaunt your |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
493 |
individualism. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
494 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
495 |
``dates(field, kind, order='ASC')`` |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
496 |
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
497 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
498 |
Returns a ``DateQuerySet`` -- a ``QuerySet`` that evaluates to a list of |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
499 |
``datetime.datetime`` objects representing all available dates of a particular |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
500 |
kind within the contents of the ``QuerySet``. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
501 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
502 |
``field`` should be the name of a ``DateField`` or ``DateTimeField`` of your |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
503 |
model. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
504 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
505 |
``kind`` should be either ``"year"``, ``"month"`` or ``"day"``. Each |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
506 |
``datetime.datetime`` object in the result list is "truncated" to the given |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
507 |
``type``. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
508 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
509 |
* ``"year"`` returns a list of all distinct year values for the field. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
510 |
* ``"month"`` returns a list of all distinct year/month values for the field. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
511 |
* ``"day"`` returns a list of all distinct year/month/day values for the field. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
512 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
513 |
``order``, which defaults to ``'ASC'``, should be either ``'ASC'`` or |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
514 |
``'DESC'``. This specifies how to order the results. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
515 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
516 |
Examples:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
517 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
518 |
>>> Entry.objects.dates('pub_date', 'year') |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
519 |
[datetime.datetime(2005, 1, 1)] |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
520 |
>>> Entry.objects.dates('pub_date', 'month') |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
521 |
[datetime.datetime(2005, 2, 1), datetime.datetime(2005, 3, 1)] |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
522 |
>>> Entry.objects.dates('pub_date', 'day') |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
523 |
[datetime.datetime(2005, 2, 20), datetime.datetime(2005, 3, 20)] |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
524 |
>>> Entry.objects.dates('pub_date', 'day', order='DESC') |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
525 |
[datetime.datetime(2005, 3, 20), datetime.datetime(2005, 2, 20)] |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
526 |
>>> Entry.objects.filter(headline__contains='Lennon').dates('pub_date', 'day') |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
527 |
[datetime.datetime(2005, 3, 20)] |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
528 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
529 |
``none()`` |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
530 |
~~~~~~~~~~ |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
531 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
532 |
**New in Django development version** |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
533 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
534 |
Returns an ``EmptyQuerySet`` -- a ``QuerySet`` that always evaluates to |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
535 |
an empty list. This can be used in cases where you know that you should |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
536 |
return an empty result set and your caller is expecting a ``QuerySet`` |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
537 |
object (instead of returning an empty list, for example.) |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
538 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
539 |
Examples:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
540 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
541 |
>>> Entry.objects.none() |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
542 |
[] |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
543 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
544 |
``select_related()`` |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
545 |
~~~~~~~~~~~~~~~~~~~~ |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
546 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
547 |
Returns a ``QuerySet`` that will automatically "follow" foreign-key |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
548 |
relationships, selecting that additional related-object data when it executes |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
549 |
its query. This is a performance booster which results in (sometimes much) |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
550 |
larger queries but means later use of foreign-key relationships won't require |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
551 |
database queries. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
552 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
553 |
The following examples illustrate the difference between plain lookups and |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
554 |
``select_related()`` lookups. Here's standard lookup:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
555 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
556 |
# Hits the database. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
557 |
e = Entry.objects.get(id=5) |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
558 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
559 |
# Hits the database again to get the related Blog object. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
560 |
b = e.blog |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
561 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
562 |
And here's ``select_related`` lookup:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
563 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
564 |
# Hits the database. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
565 |
e = Entry.objects.select_related().get(id=5) |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
566 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
567 |
# Doesn't hit the database, because e.blog has been prepopulated |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
568 |
# in the previous query. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
569 |
b = e.blog |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
570 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
571 |
``select_related()`` follows foreign keys as far as possible. If you have the |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
572 |
following models:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
573 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
574 |
class City(models.Model): |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
575 |
# ... |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
576 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
577 |
class Person(models.Model): |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
578 |
# ... |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
579 |
hometown = models.ForeignKey(City) |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
580 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
581 |
class Book(models.Model): |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
582 |
# ... |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
583 |
author = models.ForeignKey(Person) |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
584 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
585 |
...then a call to ``Book.objects.select_related().get(id=4)`` will cache the |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
586 |
related ``Person`` *and* the related ``City``:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
587 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
588 |
b = Book.objects.select_related().get(id=4) |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
589 |
p = b.author # Doesn't hit the database. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
590 |
c = p.hometown # Doesn't hit the database. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
591 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
592 |
sv = Book.objects.get(id=4) # No select_related() in this example. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
593 |
p = b.author # Hits the database. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
594 |
c = p.hometown # Hits the database. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
595 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
596 |
Note that ``select_related()`` does not follow foreign keys that have |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
597 |
``null=True``. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
598 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
599 |
Usually, using ``select_related()`` can vastly improve performance because your |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
600 |
app can avoid many database calls. However, in situations with deeply nested |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
601 |
sets of relationships ``select_related()`` can sometimes end up following "too |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
602 |
many" relations, and can generate queries so large that they end up being slow. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
603 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
604 |
In these situations, you can use the ``depth`` argument to ``select_related()`` |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
605 |
to control how many "levels" of relations ``select_related()`` will actually |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
606 |
follow:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
607 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
608 |
b = Book.objects.select_related(depth=1).get(id=4) |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
609 |
p = b.author # Doesn't hit the database. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
610 |
c = p.hometown # Requires a database call. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
611 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
612 |
The ``depth`` argument is new in the Django development version. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
613 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
614 |
``extra(select=None, where=None, params=None, tables=None)`` |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
615 |
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
616 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
617 |
Sometimes, the Django query syntax by itself can't easily express a complex |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
618 |
``WHERE`` clause. For these edge cases, Django provides the ``extra()`` |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
619 |
``QuerySet`` modifier -- a hook for injecting specific clauses into the SQL |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
620 |
generated by a ``QuerySet``. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
621 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
622 |
By definition, these extra lookups may not be portable to different database |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
623 |
engines (because you're explicitly writing SQL code) and violate the DRY |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
624 |
principle, so you should avoid them if possible. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
625 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
626 |
Specify one or more of ``params``, ``select``, ``where`` or ``tables``. None |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
627 |
of the arguments is required, but you should use at least one of them. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
628 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
629 |
``select`` |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
630 |
The ``select`` argument lets you put extra fields in the ``SELECT`` clause. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
631 |
It should be a dictionary mapping attribute names to SQL clauses to use to |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
632 |
calculate that attribute. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
633 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
634 |
Example:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
635 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
636 |
Entry.objects.extra(select={'is_recent': "pub_date > '2006-01-01'"}) |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
637 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
638 |
As a result, each ``Entry`` object will have an extra attribute, |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
639 |
``is_recent``, a boolean representing whether the entry's ``pub_date`` is |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
640 |
greater than Jan. 1, 2006. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
641 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
642 |
Django inserts the given SQL snippet directly into the ``SELECT`` |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
643 |
statement, so the resulting SQL of the above example would be:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
644 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
645 |
SELECT blog_entry.*, (pub_date > '2006-01-01') |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
646 |
FROM blog_entry; |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
647 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
648 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
649 |
The next example is more advanced; it does a subquery to give each |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
650 |
resulting ``Blog`` object an ``entry_count`` attribute, an integer count |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
651 |
of associated ``Entry`` objects:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
652 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
653 |
Blog.objects.extra( |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
654 |
select={ |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
655 |
'entry_count': 'SELECT COUNT(*) FROM blog_entry WHERE blog_entry.blog_id = blog_blog.id' |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
656 |
}, |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
657 |
) |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
658 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
659 |
(In this particular case, we're exploiting the fact that the query will |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
660 |
already contain the ``blog_blog`` table in its ``FROM`` clause.) |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
661 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
662 |
The resulting SQL of the above example would be:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
663 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
664 |
SELECT blog_blog.*, (SELECT COUNT(*) FROM blog_entry WHERE blog_entry.blog_id = blog_blog.id) |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
665 |
FROM blog_blog; |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
666 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
667 |
Note that the parenthesis required by most database engines around |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
668 |
subqueries are not required in Django's ``select`` clauses. Also note that |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
669 |
some database backends, such as some MySQL versions, don't support |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
670 |
subqueries. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
671 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
672 |
``where`` / ``tables`` |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
673 |
You can define explicit SQL ``WHERE`` clauses -- perhaps to perform |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
674 |
non-explicit joins -- by using ``where``. You can manually add tables to |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
675 |
the SQL ``FROM`` clause by using ``tables``. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
676 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
677 |
``where`` and ``tables`` both take a list of strings. All ``where`` |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
678 |
parameters are "AND"ed to any other search criteria. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
679 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
680 |
Example:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
681 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
682 |
Entry.objects.extra(where=['id IN (3, 4, 5, 20)']) |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
683 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
684 |
...translates (roughly) into the following SQL:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
685 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
686 |
SELECT * FROM blog_entry WHERE id IN (3, 4, 5, 20); |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
687 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
688 |
``params`` |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
689 |
The ``select`` and ``where`` parameters described above may use standard |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
690 |
Python database string placeholders -- ``'%s'`` to indicate parameters the |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
691 |
database engine should automatically quote. The ``params`` argument is a |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
692 |
list of any extra parameters to be substituted. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
693 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
694 |
Example:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
695 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
696 |
Entry.objects.extra(where=['headline=%s'], params=['Lennon']) |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
697 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
698 |
Always use ``params`` instead of embedding values directly into ``select`` |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
699 |
or ``where`` because ``params`` will ensure values are quoted correctly |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
700 |
according to your particular backend. (For example, quotes will be escaped |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
701 |
correctly.) |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
702 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
703 |
Bad:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
704 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
705 |
Entry.objects.extra(where=["headline='Lennon'"]) |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
706 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
707 |
Good:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
708 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
709 |
Entry.objects.extra(where=['headline=%s'], params=['Lennon']) |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
710 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
711 |
QuerySet methods that do not return QuerySets |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
712 |
--------------------------------------------- |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
713 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
714 |
The following ``QuerySet`` methods evaluate the ``QuerySet`` and return |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
715 |
something *other than* a ``QuerySet``. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
716 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
717 |
These methods do not use a cache (see _`Caching and QuerySets` below). Rather, |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
718 |
they query the database each time they're called. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
719 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
720 |
``get(**kwargs)`` |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
721 |
~~~~~~~~~~~~~~~~~ |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
722 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
723 |
Returns the object matching the given lookup parameters, which should be in |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
724 |
the format described in `Field lookups`_. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
725 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
726 |
``get()`` raises ``AssertionError`` if more than one object was found. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
727 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
728 |
``get()`` raises a ``DoesNotExist`` exception if an object wasn't found for the |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
729 |
given parameters. The ``DoesNotExist`` exception is an attribute of the model |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
730 |
class. Example:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
731 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
732 |
Entry.objects.get(id='foo') # raises Entry.DoesNotExist |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
733 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
734 |
The ``DoesNotExist`` exception inherits from |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
735 |
``django.core.exceptions.ObjectDoesNotExist``, so you can target multiple |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
736 |
``DoesNotExist`` exceptions. Example:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
737 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
738 |
from django.core.exceptions import ObjectDoesNotExist |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
739 |
try: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
740 |
e = Entry.objects.get(id=3) |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
741 |
b = Blog.objects.get(id=1) |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
742 |
except ObjectDoesNotExist: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
743 |
print "Either the entry or blog doesn't exist." |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
744 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
745 |
``create(**kwargs)`` |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
746 |
~~~~~~~~~~~~~~~~~~~~ |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
747 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
748 |
A convenience method for creating an object and saving it all in one step. Thus:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
749 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
750 |
p = Person.objects.create(first_name="Bruce", last_name="Springsteen") |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
751 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
752 |
and:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
753 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
754 |
p = Person(first_name="Bruce", last_name="Springsteen") |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
755 |
p.save() |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
756 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
757 |
are equivalent. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
758 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
759 |
``get_or_create(**kwargs)`` |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
760 |
~~~~~~~~~~~~~~~~~~~~~~~~~~~ |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
761 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
762 |
A convenience method for looking up an object with the given kwargs, creating |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
763 |
one if necessary. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
764 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
765 |
Returns a tuple of ``(object, created)``, where ``object`` is the retrieved or |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
766 |
created object and ``created`` is a boolean specifying whether a new object was |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
767 |
created. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
768 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
769 |
This is meant as a shortcut to boilerplatish code and is mostly useful for |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
770 |
data-import scripts. For example:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
771 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
772 |
try: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
773 |
obj = Person.objects.get(first_name='John', last_name='Lennon') |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
774 |
except Person.DoesNotExist: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
775 |
obj = Person(first_name='John', last_name='Lennon', birthday=date(1940, 10, 9)) |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
776 |
obj.save() |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
777 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
778 |
This pattern gets quite unwieldy as the number of fields in a model goes up. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
779 |
The above example can be rewritten using ``get_or_create()`` like so:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
780 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
781 |
obj, created = Person.objects.get_or_create(first_name='John', last_name='Lennon', |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
782 |
defaults={'birthday': date(1940, 10, 9)}) |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
783 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
784 |
Any keyword arguments passed to ``get_or_create()`` -- *except* an optional one |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
785 |
called ``defaults`` -- will be used in a ``get()`` call. If an object is found, |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
786 |
``get_or_create()`` returns a tuple of that object and ``False``. If an object |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
787 |
is *not* found, ``get_or_create()`` will instantiate and save a new object, |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
788 |
returning a tuple of the new object and ``True``. The new object will be |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
789 |
created according to this algorithm:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
790 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
791 |
defaults = kwargs.pop('defaults', {}) |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
792 |
params = dict([(k, v) for k, v in kwargs.items() if '__' not in k]) |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
793 |
params.update(defaults) |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
794 |
obj = self.model(**params) |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
795 |
obj.save() |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
796 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
797 |
In English, that means start with any non-``'defaults'`` keyword argument that |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
798 |
doesn't contain a double underscore (which would indicate a non-exact lookup). |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
799 |
Then add the contents of ``defaults``, overriding any keys if necessary, and |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
800 |
use the result as the keyword arguments to the model class. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
801 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
802 |
If you have a field named ``defaults`` and want to use it as an exact lookup in |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
803 |
``get_or_create()``, just use ``'defaults__exact'``, like so:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
804 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
805 |
Foo.objects.get_or_create(defaults__exact='bar', defaults={'defaults': 'baz'}) |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
806 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
807 |
Finally, a word on using ``get_or_create()`` in Django views. As mentioned |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
808 |
earlier, ``get_or_create()`` is mostly useful in scripts that need to parse |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
809 |
data and create new records if existing ones aren't available. But if you need |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
810 |
to use ``get_or_create()`` in a view, please make sure to use it only in |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
811 |
``POST`` requests unless you have a good reason not to. ``GET`` requests |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
812 |
shouldn't have any effect on data; use ``POST`` whenever a request to a page |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
813 |
has a side effect on your data. For more, see `Safe methods`_ in the HTTP spec. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
814 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
815 |
.. _Safe methods: http://www.w3.org/Protocols/rfc2616/rfc2616-sec9.html#sec9.1.1 |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
816 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
817 |
``count()`` |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
818 |
~~~~~~~~~~~ |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
819 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
820 |
Returns an integer representing the number of objects in the database matching |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
821 |
the ``QuerySet``. ``count()`` never raises exceptions. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
822 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
823 |
Example:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
824 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
825 |
# Returns the total number of entries in the database. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
826 |
Entry.objects.count() |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
827 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
828 |
# Returns the number of entries whose headline contains 'Lennon' |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
829 |
Entry.objects.filter(headline__contains='Lennon').count() |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
830 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
831 |
``count()`` performs a ``SELECT COUNT(*)`` behind the scenes, so you should |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
832 |
always use ``count()`` rather than loading all of the record into Python |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
833 |
objects and calling ``len()`` on the result. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
834 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
835 |
Depending on which database you're using (e.g. PostgreSQL vs. MySQL), |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
836 |
``count()`` may return a long integer instead of a normal Python integer. This |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
837 |
is an underlying implementation quirk that shouldn't pose any real-world |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
838 |
problems. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
839 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
840 |
``in_bulk(id_list)`` |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
841 |
~~~~~~~~~~~~~~~~~~~~ |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
842 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
843 |
Takes a list of primary-key values and returns a dictionary mapping each |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
844 |
primary-key value to an instance of the object with the given ID. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
845 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
846 |
Example:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
847 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
848 |
>>> Blog.objects.in_bulk([1]) |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
849 |
{1: Beatles Blog} |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
850 |
>>> Blog.objects.in_bulk([1, 2]) |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
851 |
{1: Beatles Blog, 2: Cheddar Talk} |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
852 |
>>> Blog.objects.in_bulk([]) |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
853 |
{} |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
854 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
855 |
If you pass ``in_bulk()`` an empty list, you'll get an empty dictionary. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
856 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
857 |
``latest(field_name=None)`` |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
858 |
~~~~~~~~~~~~~~~~~~~~~~~~~~~ |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
859 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
860 |
Returns the latest object in the table, by date, using the ``field_name`` |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
861 |
provided as the date field. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
862 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
863 |
This example returns the latest ``Entry`` in the table, according to the |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
864 |
``pub_date`` field:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
865 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
866 |
Entry.objects.latest('pub_date') |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
867 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
868 |
If your model's ``Meta`` specifies ``get_latest_by``, you can leave off the |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
869 |
``field_name`` argument to ``latest()``. Django will use the field specified in |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
870 |
``get_latest_by`` by default. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
871 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
872 |
Like ``get()``, ``latest()`` raises ``DoesNotExist`` if an object doesn't |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
873 |
exist with the given parameters. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
874 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
875 |
Note ``latest()`` exists purely for convenience and readability. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
876 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
877 |
Field lookups |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
878 |
------------- |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
879 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
880 |
Field lookups are how you specify the meat of an SQL ``WHERE`` clause. They're |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
881 |
specified as keyword arguments to the ``QuerySet`` methods ``filter()``, |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
882 |
``exclude()`` and ``get()``. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
883 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
884 |
Basic lookups keyword arguments take the form ``field__lookuptype=value``. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
885 |
(That's a double-underscore). For example:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
886 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
887 |
Entry.objects.filter(pub_date__lte='2006-01-01') |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
888 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
889 |
translates (roughly) into the following SQL:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
890 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
891 |
SELECT * FROM blog_entry WHERE pub_date <= '2006-01-01'; |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
892 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
893 |
.. admonition:: How this is possible |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
894 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
895 |
Python has the ability to define functions that accept arbitrary name-value |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
896 |
arguments whose names and values are evaluated at runtime. For more |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
897 |
information, see `Keyword Arguments`_ in the official Python tutorial. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
898 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
899 |
.. _`Keyword Arguments`: http://docs.python.org/tut/node6.html#SECTION006720000000000000000 |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
900 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
901 |
If you pass an invalid keyword argument, a lookup function will raise |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
902 |
``TypeError``. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
903 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
904 |
The database API supports the following lookup types: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
905 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
906 |
exact |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
907 |
~~~~~ |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
908 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
909 |
Exact match. If the value provided for comparison is ``None``, it will |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
910 |
be interpreted as an SQL ``NULL`` (See isnull_ for more details). |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
911 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
912 |
Examples:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
913 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
914 |
Entry.objects.get(id__exact=14) |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
915 |
Entry.objects.get(id__exact=None) |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
916 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
917 |
SQL equivalents:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
918 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
919 |
SELECT ... WHERE id = 14; |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
920 |
SELECT ... WHERE id = NULL; |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
921 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
922 |
iexact |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
923 |
~~~~~~ |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
924 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
925 |
Case-insensitive exact match. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
926 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
927 |
Example:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
928 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
929 |
Blog.objects.get(name__iexact='beatles blog') |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
930 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
931 |
SQL equivalent:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
932 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
933 |
SELECT ... WHERE name ILIKE 'beatles blog'; |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
934 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
935 |
Note this will match ``'Beatles Blog'``, ``'beatles blog'``, |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
936 |
``'BeAtLes BLoG'``, etc. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
937 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
938 |
contains |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
939 |
~~~~~~~~ |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
940 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
941 |
Case-sensitive containment test. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
942 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
943 |
Example:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
944 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
945 |
Entry.objects.get(headline__contains='Lennon') |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
946 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
947 |
SQL equivalent:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
948 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
949 |
SELECT ... WHERE headline LIKE '%Lennon%'; |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
950 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
951 |
Note this will match the headline ``'Today Lennon honored'`` but not |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
952 |
``'today lennon honored'``. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
953 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
954 |
SQLite doesn't support case-sensitive ``LIKE`` statements; ``contains`` acts |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
955 |
like ``icontains`` for SQLite. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
956 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
957 |
icontains |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
958 |
~~~~~~~~~ |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
959 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
960 |
Case-insensitive containment test. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
961 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
962 |
Example:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
963 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
964 |
Entry.objects.get(headline__icontains='Lennon') |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
965 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
966 |
SQL equivalent:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
967 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
968 |
SELECT ... WHERE headline ILIKE '%Lennon%'; |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
969 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
970 |
gt |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
971 |
~~ |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
972 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
973 |
Greater than. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
974 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
975 |
Example:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
976 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
977 |
Entry.objects.filter(id__gt=4) |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
978 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
979 |
SQL equivalent:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
980 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
981 |
SELECT ... WHERE id > 4; |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
982 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
983 |
gte |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
984 |
~~~ |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
985 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
986 |
Greater than or equal to. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
987 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
988 |
lt |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
989 |
~~ |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
990 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
991 |
Less than. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
992 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
993 |
lte |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
994 |
~~~ |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
995 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
996 |
Less than or equal to. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
997 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
998 |
in |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
999 |
~~ |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1000 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1001 |
In a given list. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1002 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1003 |
Example:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1004 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1005 |
Entry.objects.filter(id__in=[1, 3, 4]) |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1006 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1007 |
SQL equivalent:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1008 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1009 |
SELECT ... WHERE id IN (1, 3, 4); |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1010 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1011 |
startswith |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1012 |
~~~~~~~~~~ |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1013 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1014 |
Case-sensitive starts-with. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1015 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1016 |
Example:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1017 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1018 |
Entry.objects.filter(headline__startswith='Will') |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1019 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1020 |
SQL equivalent:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1021 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1022 |
SELECT ... WHERE headline LIKE 'Will%'; |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1023 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1024 |
SQLite doesn't support case-sensitive ``LIKE`` statements; ``startswith`` acts |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1025 |
like ``istartswith`` for SQLite. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1026 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1027 |
istartswith |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1028 |
~~~~~~~~~~~ |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1029 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1030 |
Case-insensitive starts-with. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1031 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1032 |
Example:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1033 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1034 |
Entry.objects.filter(headline__istartswith='will') |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1035 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1036 |
SQL equivalent:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1037 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1038 |
SELECT ... WHERE headline ILIKE 'Will%'; |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1039 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1040 |
endswith |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1041 |
~~~~~~~~ |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1042 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1043 |
Case-sensitive ends-with. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1044 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1045 |
Example:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1046 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1047 |
Entry.objects.filter(headline__endswith='cats') |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1048 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1049 |
SQL equivalent:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1050 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1051 |
SELECT ... WHERE headline LIKE '%cats'; |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1052 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1053 |
SQLite doesn't support case-sensitive ``LIKE`` statements; ``endswith`` acts |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1054 |
like ``iendswith`` for SQLite. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1055 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1056 |
iendswith |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1057 |
~~~~~~~~~ |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1058 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1059 |
Case-insensitive ends-with. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1060 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1061 |
Example:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1062 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1063 |
Entry.objects.filter(headline__iendswith='will') |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1064 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1065 |
SQL equivalent:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1066 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1067 |
SELECT ... WHERE headline ILIKE '%will' |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1068 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1069 |
range |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1070 |
~~~~~ |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1071 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1072 |
Range test (inclusive). |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1073 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1074 |
Example:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1075 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1076 |
start_date = datetime.date(2005, 1, 1) |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1077 |
end_date = datetime.date(2005, 3, 31) |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1078 |
Entry.objects.filter(pub_date__range=(start_date, end_date)) |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1079 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1080 |
SQL equivalent:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1081 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1082 |
SELECT ... WHERE pub_date BETWEEN '2005-01-01' and '2005-03-31'; |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1083 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1084 |
You can use ``range`` anywhere you can use ``BETWEEN`` in SQL -- for dates, |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1085 |
numbers and even characters. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1086 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1087 |
year |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1088 |
~~~~ |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1089 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1090 |
For date/datetime fields, exact year match. Takes a four-digit year. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1091 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1092 |
Example:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1093 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1094 |
Entry.objects.filter(pub_date__year=2005) |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1095 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1096 |
SQL equivalent:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1097 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1098 |
SELECT ... WHERE EXTRACT('year' FROM pub_date) = '2005'; |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1099 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1100 |
(The exact SQL syntax varies for each database engine.) |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1101 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1102 |
month |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1103 |
~~~~~ |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1104 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1105 |
For date/datetime fields, exact month match. Takes an integer 1 (January) |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1106 |
through 12 (December). |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1107 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1108 |
Example:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1109 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1110 |
Entry.objects.filter(pub_date__month=12) |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1111 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1112 |
SQL equivalent:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1113 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1114 |
SELECT ... WHERE EXTRACT('month' FROM pub_date) = '12'; |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1115 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1116 |
(The exact SQL syntax varies for each database engine.) |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1117 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1118 |
day |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1119 |
~~~ |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1120 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1121 |
For date/datetime fields, exact day match. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1122 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1123 |
Example:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1124 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1125 |
Entry.objects.filter(pub_date__day=3) |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1126 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1127 |
SQL equivalent:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1128 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1129 |
SELECT ... WHERE EXTRACT('day' FROM pub_date) = '3'; |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1130 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1131 |
(The exact SQL syntax varies for each database engine.) |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1132 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1133 |
Note this will match any record with a pub_date on the third day of the month, |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1134 |
such as January 3, July 3, etc. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1135 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1136 |
isnull |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1137 |
~~~~~~ |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1138 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1139 |
Takes either ``True`` or ``False``, which correspond to SQL queries of |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1140 |
``IS NULL`` and ``IS NOT NULL``, respectively. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1141 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1142 |
Example:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1143 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1144 |
Entry.objects.filter(pub_date__isnull=True) |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1145 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1146 |
SQL equivalent:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1147 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1148 |
SELECT ... WHERE pub_date IS NULL; |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1149 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1150 |
.. admonition:: ``__isnull=True`` vs ``__exact=None`` |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1151 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1152 |
There is an important difference between ``__isnull=True`` and |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1153 |
``__exact=None``. ``__exact=None`` will *always* return an empty result |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1154 |
set, because SQL requires that no value is equal to ``NULL``. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1155 |
``__isnull`` determines if the field is currently holding the value |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1156 |
of ``NULL`` without performing a comparison. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1157 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1158 |
search |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1159 |
~~~~~~ |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1160 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1161 |
A boolean full-text search, taking advantage of full-text indexing. This is |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1162 |
like ``contains`` but is significantly faster due to full-text indexing. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1163 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1164 |
Note this is only available in MySQL and requires direct manipulation of the |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1165 |
database to add the full-text index. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1166 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1167 |
Default lookups are exact |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1168 |
------------------------- |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1169 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1170 |
If you don't provide a lookup type -- that is, if your keyword argument doesn't |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1171 |
contain a double underscore -- the lookup type is assumed to be ``exact``. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1172 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1173 |
For example, the following two statements are equivalent:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1174 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1175 |
Blog.objects.get(id__exact=14) # Explicit form |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1176 |
Blog.objects.get(id=14) # __exact is implied |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1177 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1178 |
This is for convenience, because ``exact`` lookups are the common case. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1179 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1180 |
The pk lookup shortcut |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1181 |
---------------------- |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1182 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1183 |
For convenience, Django provides a ``pk`` lookup type, which stands for |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1184 |
"primary_key". |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1185 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1186 |
In the example ``Blog`` model, the primary key is the ``id`` field, so these |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1187 |
three statements are equivalent:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1188 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1189 |
Blog.objects.get(id__exact=14) # Explicit form |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1190 |
Blog.objects.get(id=14) # __exact is implied |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1191 |
Blog.objects.get(pk=14) # pk implies id__exact |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1192 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1193 |
The use of ``pk`` isn't limited to ``__exact`` queries -- any query term |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1194 |
can be combined with ``pk`` to perform a query on the primary key of a model:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1195 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1196 |
# Get blogs entries with id 1, 4 and 7 |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1197 |
Blog.objects.filter(pk__in=[1,4,7]) |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1198 |
# Get all blog entries with id > 14 |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1199 |
Blog.objects.filter(pk__gt=14) |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1200 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1201 |
``pk`` lookups also work across joins. For example, these three statements are |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1202 |
equivalent:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1203 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1204 |
Entry.objects.filter(blog__id__exact=3) # Explicit form |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1205 |
Entry.objects.filter(blog__id=3) # __exact is implied |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1206 |
Entry.objects.filter(blog__pk=3) # __pk implies __id__exact |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1207 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1208 |
Lookups that span relationships |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1209 |
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1210 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1211 |
Django offers a powerful and intuitive way to "follow" relationships in |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1212 |
lookups, taking care of the SQL ``JOIN``\s for you automatically, behind the |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1213 |
scenes. To span a relationship, just use the field name of related fields |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1214 |
across models, separated by double underscores, until you get to the field you |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1215 |
want. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1216 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1217 |
This example retrieves all ``Entry`` objects with a ``Blog`` whose ``name`` |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1218 |
is ``'Beatles Blog'``:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1219 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1220 |
Entry.objects.filter(blog__name__exact='Beatles Blog') |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1221 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1222 |
This spanning can be as deep as you'd like. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1223 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1224 |
It works backwards, too. To refer to a "reverse" relationship, just use the |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1225 |
lowercase name of the model. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1226 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1227 |
This example retrieves all ``Blog`` objects which have at least one ``Entry`` |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1228 |
whose ``headline`` contains ``'Lennon'``:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1229 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1230 |
Blog.objects.filter(entry__headline__contains='Lennon') |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1231 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1232 |
Escaping parenthesis and underscores in LIKE statements |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1233 |
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1234 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1235 |
The field lookups that equate to ``LIKE`` SQL statements (``iexact``, |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1236 |
``contains``, ``icontains``, ``startswith``, ``istartswith``, ``endswith`` |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1237 |
and ``iendswith``) will automatically escape the two special characters used in |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1238 |
``LIKE`` statements -- the percent sign and the underscore. (In a ``LIKE`` |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1239 |
statement, the percent sign signifies a multiple-character wildcard and the |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1240 |
underscore signifies a single-character wildcard.) |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1241 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1242 |
This means things should work intuitively, so the abstraction doesn't leak. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1243 |
For example, to retrieve all the entries that contain a percent sign, just use |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1244 |
the percent sign as any other character:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1245 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1246 |
Entry.objects.filter(headline__contains='%') |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1247 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1248 |
Django takes care of the quoting for you; the resulting SQL will look something |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1249 |
like this:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1250 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1251 |
SELECT ... WHERE headline LIKE '%\%%'; |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1252 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1253 |
Same goes for underscores. Both percentage signs and underscores are handled |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1254 |
for you transparently. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1255 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1256 |
Caching and QuerySets |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1257 |
--------------------- |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1258 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1259 |
Each ``QuerySet`` contains a cache, to minimize database access. It's important |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1260 |
to understand how it works, in order to write the most efficient code. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1261 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1262 |
In a newly created ``QuerySet``, the cache is empty. The first time a |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1263 |
``QuerySet`` is evaluated -- and, hence, a database query happens -- Django |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1264 |
saves the query results in the ``QuerySet``'s cache and returns the results |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1265 |
that have been explicitly requested (e.g., the next element, if the |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1266 |
``QuerySet`` is being iterated over). Subsequent evaluations of the |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1267 |
``QuerySet`` reuse the cached results. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1268 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1269 |
Keep this caching behavior in mind, because it may bite you if you don't use |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1270 |
your ``QuerySet``\s correctly. For example, the following will create two |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1271 |
``QuerySet``\s, evaluate them, and throw them away:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1272 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1273 |
print [e.headline for e in Entry.objects.all()] |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1274 |
print [e.pub_date for e in Entry.objects.all()] |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1275 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1276 |
That means the same database query will be executed twice, effectively doubling |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1277 |
your database load. Also, there's a possibility the two lists may not include |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1278 |
the same database records, because an ``Entry`` may have been added or deleted |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1279 |
in the split second between the two requests. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1280 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1281 |
To avoid this problem, simply save the ``QuerySet`` and reuse it:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1282 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1283 |
queryset = Poll.objects.all() |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1284 |
print [p.headline for p in queryset] # Evaluate the query set. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1285 |
print [p.pub_date for p in queryset] # Re-use the cache from the evaluation. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1286 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1287 |
Comparing objects |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1288 |
================= |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1289 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1290 |
To compare two model instances, just use the standard Python comparison operator, |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1291 |
the double equals sign: ``==``. Behind the scenes, that compares the primary |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1292 |
key values of two models. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1293 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1294 |
Using the ``Entry`` example above, the following two statements are equivalent:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1295 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1296 |
some_entry == other_entry |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1297 |
some_entry.id == other_entry.id |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1298 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1299 |
If a model's primary key isn't called ``id``, no problem. Comparisons will |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1300 |
always use the primary key, whatever it's called. For example, if a model's |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1301 |
primary key field is called ``name``, these two statements are equivalent:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1302 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1303 |
some_obj == other_obj |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1304 |
some_obj.name == other_obj.name |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1305 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1306 |
Complex lookups with Q objects |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1307 |
============================== |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1308 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1309 |
Keyword argument queries -- in ``filter()``, etc. -- are "AND"ed together. If |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1310 |
you need to execute more complex queries (for example, queries with ``OR`` |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1311 |
statements), you can use ``Q`` objects. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1312 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1313 |
A ``Q`` object (``django.db.models.Q``) is an object used to encapsulate a |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1314 |
collection of keyword arguments. These keyword arguments are specified as in |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1315 |
"Field lookups" above. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1316 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1317 |
For example, this ``Q`` object encapsulates a single ``LIKE`` query:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1318 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1319 |
Q(question__startswith='What') |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1320 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1321 |
``Q`` objects can be combined using the ``&`` and ``|`` operators. When an |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1322 |
operator is used on two ``Q`` objects, it yields a new ``Q`` object. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1323 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1324 |
For example, this statement yields a single ``Q`` object that represents the |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1325 |
"OR" of two ``"question__startswith"`` queries:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1326 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1327 |
Q(question__startswith='Who') | Q(question__startswith='What') |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1328 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1329 |
This is equivalent to the following SQL ``WHERE`` clause:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1330 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1331 |
WHERE question LIKE 'Who%' OR question LIKE 'What%' |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1332 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1333 |
You can compose statements of arbitrary complexity by combining ``Q`` objects |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1334 |
with the ``&`` and ``|`` operators. You can also use parenthetical grouping. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1335 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1336 |
Each lookup function that takes keyword-arguments (e.g. ``filter()``, |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1337 |
``exclude()``, ``get()``) can also be passed one or more ``Q`` objects as |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1338 |
positional (not-named) arguments. If you provide multiple ``Q`` object |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1339 |
arguments to a lookup function, the arguments will be "AND"ed together. For |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1340 |
example:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1341 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1342 |
Poll.objects.get( |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1343 |
Q(question__startswith='Who'), |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1344 |
Q(pub_date=date(2005, 5, 2)) | Q(pub_date=date(2005, 5, 6)) |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1345 |
) |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1346 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1347 |
... roughly translates into the SQL:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1348 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1349 |
SELECT * from polls WHERE question LIKE 'Who%' |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1350 |
AND (pub_date = '2005-05-02' OR pub_date = '2005-05-06') |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1351 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1352 |
Lookup functions can mix the use of ``Q`` objects and keyword arguments. All |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1353 |
arguments provided to a lookup function (be they keyword arguments or ``Q`` |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1354 |
objects) are "AND"ed together. However, if a ``Q`` object is provided, it must |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1355 |
precede the definition of any keyword arguments. For example:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1356 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1357 |
Poll.objects.get( |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1358 |
Q(pub_date=date(2005, 5, 2)) | Q(pub_date=date(2005, 5, 6)), |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1359 |
question__startswith='Who') |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1360 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1361 |
... would be a valid query, equivalent to the previous example; but:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1362 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1363 |
# INVALID QUERY |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1364 |
Poll.objects.get( |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1365 |
question__startswith='Who', |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1366 |
Q(pub_date=date(2005, 5, 2)) | Q(pub_date=date(2005, 5, 6))) |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1367 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1368 |
... would not be valid. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1369 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1370 |
See the `OR lookups examples page`_ for more examples. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1371 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1372 |
.. _OR lookups examples page: http://www.djangoproject.com/documentation/models/or_lookups/ |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1373 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1374 |
Related objects |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1375 |
=============== |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1376 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1377 |
When you define a relationship in a model (i.e., a ``ForeignKey``, |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1378 |
``OneToOneField``, or ``ManyToManyField``), instances of that model will have |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1379 |
a convenient API to access the related object(s). |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1380 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1381 |
Using the models at the top of this page, for example, an ``Entry`` object ``e`` |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1382 |
can get its associated ``Blog`` object by accessing the ``blog`` attribute: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1383 |
``e.blog``. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1384 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1385 |
(Behind the scenes, this functionality is implemented by Python descriptors_. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1386 |
This shouldn't really matter to you, but we point it out here for the curious.) |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1387 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1388 |
Django also creates API accessors for the "other" side of the relationship -- |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1389 |
the link from the related model to the model that defines the relationship. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1390 |
For example, a ``Blog`` object ``b`` has access to a list of all related |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1391 |
``Entry`` objects via the ``entry_set`` attribute: ``b.entry_set.all()``. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1392 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1393 |
All examples in this section use the sample ``Blog``, ``Author`` and ``Entry`` |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1394 |
models defined at the top of this page. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1395 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1396 |
.. _descriptors: http://users.rcn.com/python/download/Descriptor.htm |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1397 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1398 |
One-to-many relationships |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1399 |
------------------------- |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1400 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1401 |
Forward |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1402 |
~~~~~~~ |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1403 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1404 |
If a model has a ``ForeignKey``, instances of that model will have access to |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1405 |
the related (foreign) object via a simple attribute of the model. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1406 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1407 |
Example:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1408 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1409 |
e = Entry.objects.get(id=2) |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1410 |
e.blog # Returns the related Blog object. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1411 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1412 |
You can get and set via a foreign-key attribute. As you may expect, changes to |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1413 |
the foreign key aren't saved to the database until you call ``save()``. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1414 |
Example:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1415 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1416 |
e = Entry.objects.get(id=2) |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1417 |
e.blog = some_blog |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1418 |
e.save() |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1419 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1420 |
If a ``ForeignKey`` field has ``null=True`` set (i.e., it allows ``NULL`` |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1421 |
values), you can assign ``None`` to it. Example:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1422 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1423 |
e = Entry.objects.get(id=2) |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1424 |
e.blog = None |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1425 |
e.save() # "UPDATE blog_entry SET blog_id = NULL ...;" |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1426 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1427 |
Forward access to one-to-many relationships is cached the first time the |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1428 |
related object is accessed. Subsequent accesses to the foreign key on the same |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1429 |
object instance are cached. Example:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1430 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1431 |
e = Entry.objects.get(id=2) |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1432 |
print e.blog # Hits the database to retrieve the associated Blog. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1433 |
print e.blog # Doesn't hit the database; uses cached version. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1434 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1435 |
Note that the ``select_related()`` ``QuerySet`` method recursively prepopulates |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1436 |
the cache of all one-to-many relationships ahead of time. Example:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1437 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1438 |
e = Entry.objects.select_related().get(id=2) |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1439 |
print e.blog # Doesn't hit the database; uses cached version. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1440 |
print e.blog # Doesn't hit the database; uses cached version. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1441 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1442 |
``select_related()`` is documented in the "QuerySet methods that return new |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1443 |
QuerySets" section above. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1444 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1445 |
Backward |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1446 |
~~~~~~~~ |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1447 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1448 |
If a model has a ``ForeignKey``, instances of the foreign-key model will have |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1449 |
access to a ``Manager`` that returns all instances of the first model. By |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1450 |
default, this ``Manager`` is named ``FOO_set``, where ``FOO`` is the source |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1451 |
model name, lowercased. This ``Manager`` returns ``QuerySets``, which can be |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1452 |
filtered and manipulated as described in the "Retrieving objects" section |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1453 |
above. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1454 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1455 |
Example:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1456 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1457 |
b = Blog.objects.get(id=1) |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1458 |
b.entry_set.all() # Returns all Entry objects related to Blog. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1459 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1460 |
# b.entry_set is a Manager that returns QuerySets. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1461 |
b.entry_set.filter(headline__contains='Lennon') |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1462 |
b.entry_set.count() |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1463 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1464 |
You can override the ``FOO_set`` name by setting the ``related_name`` |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1465 |
parameter in the ``ForeignKey()`` definition. For example, if the ``Entry`` |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1466 |
model was altered to ``blog = ForeignKey(Blog, related_name='entries')``, the |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1467 |
above example code would look like this:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1468 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1469 |
b = Blog.objects.get(id=1) |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1470 |
b.entries.all() # Returns all Entry objects related to Blog. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1471 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1472 |
# b.entries is a Manager that returns QuerySets. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1473 |
b.entries.filter(headline__contains='Lennon') |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1474 |
b.entries.count() |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1475 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1476 |
You cannot access a reverse ``ForeignKey`` ``Manager`` from the class; it must |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1477 |
be accessed from an instance. Example:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1478 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1479 |
Blog.entry_set # Raises AttributeError: "Manager must be accessed via instance". |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1480 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1481 |
In addition to the ``QuerySet`` methods defined in "Retrieving objects" above, |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1482 |
the ``ForeignKey`` ``Manager`` has these additional methods: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1483 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1484 |
* ``add(obj1, obj2, ...)``: Adds the specified model objects to the related |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1485 |
object set. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1486 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1487 |
Example:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1488 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1489 |
b = Blog.objects.get(id=1) |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1490 |
e = Entry.objects.get(id=234) |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1491 |
b.entry_set.add(e) # Associates Entry e with Blog b. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1492 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1493 |
* ``create(**kwargs)``: Creates a new object, saves it and puts it in the |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1494 |
related object set. Returns the newly created object. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1495 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1496 |
Example:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1497 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1498 |
b = Blog.objects.get(id=1) |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1499 |
e = b.entry_set.create(headline='Hello', body_text='Hi', pub_date=datetime.date(2005, 1, 1)) |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1500 |
# No need to call e.save() at this point -- it's already been saved. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1501 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1502 |
This is equivalent to (but much simpler than):: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1503 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1504 |
b = Blog.objects.get(id=1) |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1505 |
e = Entry(blog=b, headline='Hello', body_text='Hi', pub_date=datetime.date(2005, 1, 1)) |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1506 |
e.save() |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1507 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1508 |
Note that there's no need to specify the keyword argument of the model |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1509 |
that defines the relationship. In the above example, we don't pass the |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1510 |
parameter ``blog`` to ``create()``. Django figures out that the new |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1511 |
``Entry`` object's ``blog`` field should be set to ``b``. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1512 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1513 |
* ``remove(obj1, obj2, ...)``: Removes the specified model objects from the |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1514 |
related object set. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1515 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1516 |
Example:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1517 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1518 |
b = Blog.objects.get(id=1) |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1519 |
e = Entry.objects.get(id=234) |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1520 |
b.entry_set.remove(e) # Disassociates Entry e from Blog b. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1521 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1522 |
In order to prevent database inconsistency, this method only exists on |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1523 |
``ForeignKey`` objects where ``null=True``. If the related field can't be |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1524 |
set to ``None`` (``NULL``), then an object can't be removed from a |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1525 |
relation without being added to another. In the above example, removing |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1526 |
``e`` from ``b.entry_set()`` is equivalent to doing ``e.blog = None``, |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1527 |
and because the ``blog`` ``ForeignKey`` doesn't have ``null=True``, this |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1528 |
is invalid. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1529 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1530 |
* ``clear()``: Removes all objects from the related object set. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1531 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1532 |
Example:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1533 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1534 |
b = Blog.objects.get(id=1) |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1535 |
b.entry_set.clear() |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1536 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1537 |
Note this doesn't delete the related objects -- it just disassociates |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1538 |
them. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1539 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1540 |
Just like ``remove()``, ``clear()`` is only available on ``ForeignKey``s |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1541 |
where ``null=True``. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1542 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1543 |
To assign the members of a related set in one fell swoop, just assign to it |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1544 |
from any iterable object. Example:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1545 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1546 |
b = Blog.objects.get(id=1) |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1547 |
b.entry_set = [e1, e2] |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1548 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1549 |
If the ``clear()`` method is available, any pre-existing objects will be |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1550 |
removed from the ``entry_set`` before all objects in the iterable (in this |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1551 |
case, a list) are added to the set. If the ``clear()`` method is *not* |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1552 |
available, all objects in the iterable will be added without removing any |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1553 |
existing elements. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1554 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1555 |
Each "reverse" operation described in this section has an immediate effect on |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1556 |
the database. Every addition, creation and deletion is immediately and |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1557 |
automatically saved to the database. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1558 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1559 |
Many-to-many relationships |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1560 |
-------------------------- |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1561 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1562 |
Both ends of a many-to-many relationship get automatic API access to the other |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1563 |
end. The API works just as a "backward" one-to-many relationship. See Backward_ |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1564 |
above. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1565 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1566 |
The only difference is in the attribute naming: The model that defines the |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1567 |
``ManyToManyField`` uses the attribute name of that field itself, whereas the |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1568 |
"reverse" model uses the lowercased model name of the original model, plus |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1569 |
``'_set'`` (just like reverse one-to-many relationships). |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1570 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1571 |
An example makes this easier to understand:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1572 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1573 |
e = Entry.objects.get(id=3) |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1574 |
e.authors.all() # Returns all Author objects for this Entry. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1575 |
e.authors.count() |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1576 |
e.authors.filter(name__contains='John') |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1577 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1578 |
a = Author.objects.get(id=5) |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1579 |
a.entry_set.all() # Returns all Entry objects for this Author. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1580 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1581 |
Like ``ForeignKey``, ``ManyToManyField`` can specify ``related_name``. In the |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1582 |
above example, if the ``ManyToManyField`` in ``Entry`` had specified |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1583 |
``related_name='entries'``, then each ``Author`` instance would have an |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1584 |
``entries`` attribute instead of ``entry_set``. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1585 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1586 |
One-to-one relationships |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1587 |
------------------------ |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1588 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1589 |
The semantics of one-to-one relationships will be changing soon, so we don't |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1590 |
recommend you use them. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1591 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1592 |
How are the backward relationships possible? |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1593 |
-------------------------------------------- |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1594 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1595 |
Other object-relational mappers require you to define relationships on both |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1596 |
sides. The Django developers believe this is a violation of the DRY (Don't |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1597 |
Repeat Yourself) principle, so Django only requires you to define the |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1598 |
relationship on one end. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1599 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1600 |
But how is this possible, given that a model class doesn't know which other |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1601 |
model classes are related to it until those other model classes are loaded? |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1602 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1603 |
The answer lies in the ``INSTALLED_APPS`` setting. The first time any model is |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1604 |
loaded, Django iterates over every model in ``INSTALLED_APPS`` and creates the |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1605 |
backward relationships in memory as needed. Essentially, one of the functions |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1606 |
of ``INSTALLED_APPS`` is to tell Django the entire model domain. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1607 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1608 |
Queries over related objects |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1609 |
---------------------------- |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1610 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1611 |
Queries involving related objects follow the same rules as queries involving |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1612 |
normal value fields. When specifying the the value for a query to match, you |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1613 |
may use either an object instance itself, or the primary key value for the |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1614 |
object. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1615 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1616 |
For example, if you have a Blog object ``b`` with ``id=5``, the following |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1617 |
three queries would be identical:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1618 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1619 |
Entry.objects.filter(blog=b) # Query using object instance |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1620 |
Entry.objects.filter(blog=b.id) # Query using id from instance |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1621 |
Entry.objects.filter(blog=5) # Query using id directly |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1622 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1623 |
Deleting objects |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1624 |
================ |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1625 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1626 |
The delete method, conveniently, is named ``delete()``. This method immediately |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1627 |
deletes the object and has no return value. Example:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1628 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1629 |
e.delete() |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1630 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1631 |
You can also delete objects in bulk. Every ``QuerySet`` has a ``delete()`` |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1632 |
method, which deletes all members of that ``QuerySet``. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1633 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1634 |
For example, this deletes all ``Entry`` objects with a ``pub_date`` year of |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1635 |
2005:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1636 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1637 |
Entry.objects.filter(pub_date__year=2005).delete() |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1638 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1639 |
When Django deletes an object, it emulates the behavior of the SQL |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1640 |
constraint ``ON DELETE CASCADE`` -- in other words, any objects which |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1641 |
had foreign keys pointing at the object to be deleted will be deleted |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1642 |
along with it. For example:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1643 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1644 |
b = Blog.objects.get(pk=1) |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1645 |
# This will delete the Blog and all of its Entry objects. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1646 |
b.delete() |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1647 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1648 |
Note that ``delete()`` is the only ``QuerySet`` method that is not exposed on a |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1649 |
``Manager`` itself. This is a safety mechanism to prevent you from accidentally |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1650 |
requesting ``Entry.objects.delete()``, and deleting *all* the entries. If you |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1651 |
*do* want to delete all the objects, then you have to explicitly request a |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1652 |
complete query set:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1653 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1654 |
Entry.objects.all().delete() |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1655 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1656 |
Extra instance methods |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1657 |
====================== |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1658 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1659 |
In addition to ``save()``, ``delete()``, a model object might get any or all |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1660 |
of the following methods: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1661 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1662 |
get_FOO_display() |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1663 |
----------------- |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1664 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1665 |
For every field that has ``choices`` set, the object will have a |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1666 |
``get_FOO_display()`` method, where ``FOO`` is the name of the field. This |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1667 |
method returns the "human-readable" value of the field. For example, in the |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1668 |
following model:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1669 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1670 |
GENDER_CHOICES = ( |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1671 |
('M', 'Male'), |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1672 |
('F', 'Female'), |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1673 |
) |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1674 |
class Person(models.Model): |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1675 |
name = models.CharField(maxlength=20) |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1676 |
gender = models.CharField(maxlength=1, choices=GENDER_CHOICES) |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1677 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1678 |
...each ``Person`` instance will have a ``get_gender_display()`` method. Example:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1679 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1680 |
>>> p = Person(name='John', gender='M') |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1681 |
>>> p.save() |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1682 |
>>> p.gender |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1683 |
'M' |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1684 |
>>> p.get_gender_display() |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1685 |
'Male' |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1686 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1687 |
get_next_by_FOO(\**kwargs) and get_previous_by_FOO(\**kwargs) |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1688 |
------------------------------------------------------------- |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1689 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1690 |
For every ``DateField`` and ``DateTimeField`` that does not have ``null=True``, |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1691 |
the object will have ``get_next_by_FOO()`` and ``get_previous_by_FOO()`` |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1692 |
methods, where ``FOO`` is the name of the field. This returns the next and |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1693 |
previous object with respect to the date field, raising the appropriate |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1694 |
``DoesNotExist`` exception when appropriate. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1695 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1696 |
Both methods accept optional keyword arguments, which should be in the format |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1697 |
described in `Field lookups`_ above. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1698 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1699 |
Note that in the case of identical date values, these methods will use the ID |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1700 |
as a fallback check. This guarantees that no records are skipped or duplicated. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1701 |
For a full example, see the `lookup API sample model`_. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1702 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1703 |
.. _lookup API sample model: http://www.djangoproject.com/documentation/models/lookup/ |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1704 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1705 |
get_FOO_filename() |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1706 |
------------------ |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1707 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1708 |
For every ``FileField``, the object will have a ``get_FOO_filename()`` method, |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1709 |
where ``FOO`` is the name of the field. This returns the full filesystem path |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1710 |
to the file, according to your ``MEDIA_ROOT`` setting. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1711 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1712 |
Note that ``ImageField`` is technically a subclass of ``FileField``, so every |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1713 |
model with an ``ImageField`` will also get this method. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1714 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1715 |
get_FOO_url() |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1716 |
------------- |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1717 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1718 |
For every ``FileField``, the object will have a ``get_FOO_url()`` method, |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1719 |
where ``FOO`` is the name of the field. This returns the full URL to the file, |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1720 |
according to your ``MEDIA_URL`` setting. If the value is blank, this method |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1721 |
returns an empty string. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1722 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1723 |
get_FOO_size() |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1724 |
-------------- |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1725 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1726 |
For every ``FileField``, the object will have a ``get_FOO_size()`` method, |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1727 |
where ``FOO`` is the name of the field. This returns the size of the file, in |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1728 |
bytes. (Behind the scenes, it uses ``os.path.getsize``.) |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1729 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1730 |
save_FOO_file(filename, raw_contents) |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1731 |
------------------------------------- |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1732 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1733 |
For every ``FileField``, the object will have a ``save_FOO_file()`` method, |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1734 |
where ``FOO`` is the name of the field. This saves the given file to the |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1735 |
filesystem, using the given filename. If a file with the given filename already |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1736 |
exists, Django adds an underscore to the end of the filename (but before the |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1737 |
extension) until the filename is available. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1738 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1739 |
get_FOO_height() and get_FOO_width() |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1740 |
------------------------------------ |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1741 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1742 |
For every ``ImageField``, the object will have ``get_FOO_height()`` and |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1743 |
``get_FOO_width()`` methods, where ``FOO`` is the name of the field. This |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1744 |
returns the height (or width) of the image, as an integer, in pixels. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1745 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1746 |
Shortcuts |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1747 |
========= |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1748 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1749 |
As you develop views, you will discover a number of common idioms in the |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1750 |
way you use the database API. Django encodes some of these idioms as |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1751 |
shortcuts that can be used to simplify the process of writing views. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1752 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1753 |
get_object_or_404() |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1754 |
------------------- |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1755 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1756 |
One common idiom to use ``get()`` and raise ``Http404`` if the |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1757 |
object doesn't exist. This idiom is captured by ``get_object_or_404()``. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1758 |
This function takes a Django model as its first argument and an |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1759 |
arbitrary number of keyword arguments, which it passes to the manager's |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1760 |
``get()`` function. It raises ``Http404`` if the object doesn't |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1761 |
exist. For example:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1762 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1763 |
# Get the Entry with a primary key of 3 |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1764 |
e = get_object_or_404(Entry, pk=3) |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1765 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1766 |
When you provide a model to this shortcut function, the default manager |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1767 |
is used to execute the underlying ``get()`` query. If you don't want to |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1768 |
use the default manager, or you want to search a list of related objects, |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1769 |
you can provide ``get_object_or_404()`` with a manager object, instead. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1770 |
For example:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1771 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1772 |
# Get the author of blog instance `e` with a name of 'Fred' |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1773 |
a = get_object_or_404(e.authors, name='Fred') |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1774 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1775 |
# Use a custom manager 'recent_entries' in the search for an |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1776 |
# entry with a primary key of 3 |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1777 |
e = get_object_or_404(Entry.recent_entries, pk=3) |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1778 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1779 |
get_list_or_404() |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1780 |
----------------- |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1781 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1782 |
``get_list_or_404`` behaves the same was as ``get_object_or_404()`` |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1783 |
-- except the it uses using ``filter()`` instead of ``get()``. It raises |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1784 |
``Http404`` if the list is empty. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1785 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1786 |
Falling back to raw SQL |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1787 |
======================= |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1788 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1789 |
If you find yourself needing to write an SQL query that is too complex for |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1790 |
Django's database-mapper to handle, you can fall back into raw-SQL statement |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1791 |
mode. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1792 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1793 |
The preferred way to do this is by giving your model custom methods or custom |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1794 |
manager methods that execute queries. Although there's nothing in Django that |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1795 |
*requires* database queries to live in the model layer, this approach keeps all |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1796 |
your data-access logic in one place, which is smart from an code-organization |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1797 |
standpoint. For instructions, see `Executing custom SQL`_. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1798 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1799 |
Finally, it's important to note that the Django database layer is merely an |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1800 |
interface to your database. You can access your database via other tools, |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1801 |
programming languages or database frameworks; there's nothing Django-specific |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1802 |
about your database. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1803 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
1804 |
.. _Executing custom SQL: ../model_api/#executing-custom-sql |