thirdparty/google_appengine/lib/django/docs/db-api.txt
author Lennard de Rijk <ljvderijk@gmail.com>
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======================
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Database API reference
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======================
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Once you've created your `data models`_, Django automatically gives you a
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database-abstraction API that lets you create, retrieve, update and delete
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objects. This document explains that API.
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.. _`data models`: ../model_api/
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Throughout this reference, we'll refer to the following models, which comprise
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a weblog application::
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    class Blog(models.Model):
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        name = models.CharField(maxlength=100)
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        tagline = models.TextField()
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        def __str__(self):
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            return self.name
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    class Author(models.Model):
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        name = models.CharField(maxlength=50)
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        email = models.URLField()
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        def __str__(self):
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            return self.name
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    class Entry(models.Model):
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        blog = models.ForeignKey(Blog)
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        headline = models.CharField(maxlength=255)
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        body_text = models.TextField()
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        pub_date = models.DateTimeField()
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        authors = models.ManyToManyField(Author)
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        def __str__(self):
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            return self.headline
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Creating objects
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================
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To represent database-table data in Python objects, Django uses an intuitive
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system: A model class represents a database table, and an instance of that
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class represents a particular record in the database table.
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To create an object, instantiate it using keyword arguments to the model class,
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then call ``save()`` to save it to the database.
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You import the model class from wherever it lives on the Python path, as you
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may expect. (We point this out here because previous Django versions required
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funky model importing.)
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Assuming models live in a file ``mysite/blog/models.py``, here's an example::
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    from mysite.blog.models import Blog
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    b = Blog(name='Beatles Blog', tagline='All the latest Beatles news.')
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    b.save()
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This performs an ``INSERT`` SQL statement behind the scenes. Django doesn't hit
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the database until you explicitly call ``save()``.
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The ``save()`` method has no return value.
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To create an object and save it all in one step see the `create`__ method.
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__ `create(**kwargs)`_
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Auto-incrementing primary keys
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------------------------------
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If a model has an ``AutoField`` -- an auto-incrementing primary key -- then
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that auto-incremented value will be calculated and saved as an attribute on
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your object the first time you call ``save()``.
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Example::
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    b2 = Blog(name='Cheddar Talk', tagline='Thoughts on cheese.')
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    b2.id     # Returns None, because b doesn't have an ID yet.
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    b2.save()
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    b2.id     # Returns the ID of your new object.
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There's no way to tell what the value of an ID will be before you call
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``save()``, because that value is calculated by your database, not by Django.
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(For convenience, each model has an ``AutoField`` named ``id`` by default
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unless you explicitly specify ``primary_key=True`` on a field. See the
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`AutoField documentation`_.)
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.. _AutoField documentation: ../model_api/#autofield
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Explicitly specifying auto-primary-key values
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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If a model has an ``AutoField`` but you want to define a new object's ID
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explicitly when saving, just define it explicitly before saving, rather than
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relying on the auto-assignment of the ID.
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Example::
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    b3 = Blog(id=3, name='Cheddar Talk', tagline='Thoughts on cheese.')
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    b3.id     # Returns 3.
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    b3.save()
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    b3.id     # Returns 3.
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If you assign auto-primary-key values manually, make sure not to use an
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already-existing primary-key value! If you create a new object with an explicit
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primary-key value that already exists in the database, Django will assume
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you're changing the existing record rather than creating a new one.
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Given the above ``'Cheddar Talk'`` blog example, this example would override
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the previous record in the database::
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    b4 = Blog(id=3, name='Not Cheddar', tagline='Anything but cheese.')
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    b4.save()  # Overrides the previous blog with ID=3!
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See _`How Django knows to UPDATE vs. INSERT`, below, for the reason this
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happens.
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Explicitly specifying auto-primary-key values is mostly useful for bulk-saving
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objects, when you're confident you won't have primary-key collision.
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Saving changes to objects
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=========================
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To save changes to an object that's already in the database, use ``save()``.
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Given a ``Blog`` instance ``b5`` that has already been saved to the database,
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this example changes its name and updates its record in the database::
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    b5.name = 'New name'
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    b5.save()
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This performs an ``UPDATE`` SQL statement behind the scenes. Django doesn't hit
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the database until you explicitly call ``save()``.
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The ``save()`` method has no return value.
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How Django knows to UPDATE vs. INSERT
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-------------------------------------
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You may have noticed Django database objects use the same ``save()`` method
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for creating and changing objects. Django abstracts the need to use ``INSERT``
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or ``UPDATE`` SQL statements. Specifically, when you call ``save()``, Django
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follows this algorithm:
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    * If the object's primary key attribute is set to a value that evaluates to
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      ``True`` (i.e., a value other than ``None`` or the empty string), Django 
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      executes a ``SELECT`` query to determine whether a record with the given 
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      primary key already exists.
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    * If the record with the given primary key does already exist, Django
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      executes an ``UPDATE`` query.
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    * If the object's primary key attribute is *not* set, or if it's set but a
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      record doesn't exist, Django executes an ``INSERT``.
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The one gotcha here is that you should be careful not to specify a primary-key
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value explicitly when saving new objects, if you cannot guarantee the
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primary-key value is unused. For more on this nuance, see
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"Explicitly specifying auto-primary-key values" above.
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Retrieving objects
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==================
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To retrieve objects from your database, you construct a ``QuerySet`` via a
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``Manager`` on your model class.
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A ``QuerySet`` represents a collection of objects from your database. It can
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have zero, one or many *filters* -- criteria that narrow down the collection
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based on given parameters. In SQL terms, a ``QuerySet`` equates to a ``SELECT``
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statement, and a filter is a limiting clause such as ``WHERE`` or ``LIMIT``.
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You get a ``QuerySet`` by using your model's ``Manager``. Each model has at
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least one ``Manager``, and it's called ``objects`` by default. Access it
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directly via the model class, like so::
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    Blog.objects  # <django.db.models.manager.Manager object at ...>
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    b = Blog(name='Foo', tagline='Bar')
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    b.objects     # AttributeError: "Manager isn't accessible via Blog instances."
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(``Managers`` are accessible only via model classes, rather than from model
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instances, to enforce a separation between "table-level" operations and
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"record-level" operations.)
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The ``Manager`` is the main source of ``QuerySets`` for a model. It acts as a
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"root" ``QuerySet`` that describes all objects in the model's database table.
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For example, ``Blog.objects`` is the initial ``QuerySet`` that contains all
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``Blog`` objects in the database.
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Retrieving all objects
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----------------------
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The simplest way to retrieve objects from a table is to get all of them.
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To do this, use the ``all()`` method on a ``Manager``.
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Example::
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    all_entries = Entry.objects.all()
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The ``all()`` method returns a ``QuerySet`` of all the objects in the database.
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(If ``Entry.objects`` is a ``QuerySet``, why can't we just do ``Entry.objects``?
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That's because ``Entry.objects``, the root ``QuerySet``, is a special case
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that cannot be evaluated. The ``all()`` method returns a ``QuerySet`` that
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*can* be evaluated.)
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Filtering objects
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-----------------
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The root ``QuerySet`` provided by the ``Manager`` describes all objects in the
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database table. Usually, though, you'll need to select only a subset of the
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complete set of objects.
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To create such a subset, you refine the initial ``QuerySet``, adding filter
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conditions. The two most common ways to refine a ``QuerySet`` are:
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``filter(**kwargs)``
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    Returns a new ``QuerySet`` containing objects that match the given lookup
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    parameters.
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``exclude(**kwargs)``
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    Returns a new ``QuerySet`` containing objects that do *not* match the given
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    lookup parameters.
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The lookup parameters (``**kwargs`` in the above function definitions) should
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be in the format described in `Field lookups`_ below.
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For example, to get a ``QuerySet`` of blog entries from the year 2006, use
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``filter()`` like so::
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    Entry.objects.filter(pub_date__year=2006)
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(Note we don't have to add an ``all()`` -- ``Entry.objects.all().filter(...)``.
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That would still work, but you only need ``all()`` when you want all objects
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from the root ``QuerySet``.)
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Chaining filters
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~~~~~~~~~~~~~~~~
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The result of refining a ``QuerySet`` is itself a ``QuerySet``, so it's
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possible to chain refinements together. For example::
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    Entry.objects.filter(
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        headline__startswith='What').exclude(
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            pub_date__gte=datetime.now()).filter(
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                pub_date__gte=datetime(2005, 1, 1))
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...takes the initial ``QuerySet`` of all entries in the database, adds a
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filter, then an exclusion, then another filter. The final result is a
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``QuerySet`` containing all entries with a headline that starts with "What",
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that were published between January 1, 2005, and the current day.
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Filtered QuerySets are unique
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-----------------------------
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Each time you refine a ``QuerySet``, you get a brand-new ``QuerySet`` that is
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in no way bound to the previous ``QuerySet``. Each refinement creates a
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separate and distinct ``QuerySet`` that can be stored, used and reused.
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Example::
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    q1 = Entry.objects.filter(headline__startswith="What")
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    q2 = q1.exclude(pub_date__gte=datetime.now())
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    q3 = q1.filter(pub_date__gte=datetime.now())
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These three ``QuerySets`` are separate. The first is a base ``QuerySet``
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containing all entries that contain a headline starting with "What". The second
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is a subset of the first, with an additional criteria that excludes records
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whose ``pub_date`` is greater than now. The third is a subset of the first,
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with an additional criteria that selects only the records whose ``pub_date`` is
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greater than now. The initial ``QuerySet`` (``q1``) is unaffected by the
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refinement process.
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QuerySets are lazy
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------------------
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``QuerySets`` are lazy -- the act of creating a ``QuerySet`` doesn't involve
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any database activity. You can stack filters together all day long, and Django
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won't actually run the query until the ``QuerySet`` is *evaluated*.
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When QuerySets are evaluated
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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You can evaluate a ``QuerySet`` in the following ways:
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    * **Iteration.** A ``QuerySet`` is iterable, and it executes its database
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      query the first time you iterate over it. For example, this will print
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      the headline of all entries in the database::
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          for e in Entry.objects.all():
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              print e.headline
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    * **Slicing.** As explained in `Limiting QuerySets`_ below, a ``QuerySet``
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      can be sliced, using Python's array-slicing syntax. Usually slicing a
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      ``QuerySet`` returns another (unevaluated )``QuerySet``, but Django will
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      execute the database query if you use the "step" parameter of slice
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      syntax.
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    * **repr().** A ``QuerySet`` is evaluated when you call ``repr()`` on it.
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      This is for convenience in the Python interactive interpreter, so you can
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      immediately see your results when using the API interactively.
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    * **len().** A ``QuerySet`` is evaluated when you call ``len()`` on it.
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      This, as you might expect, returns the length of the result list.
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      Note: *Don't* use ``len()`` on ``QuerySet``\s if all you want to do is
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      determine the number of records in the set. It's much more efficient to
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      handle a count at the database level, using SQL's ``SELECT COUNT(*)``,
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      and Django provides a ``count()`` method for precisely this reason. See
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      ``count()`` below.
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    * **list().** Force evaluation of a ``QuerySet`` by calling ``list()`` on
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      it. For example::
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          entry_list = list(Entry.objects.all())
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      Be warned, though, that this could have a large memory overhead, because
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      Django will load each element of the list into memory. In contrast,
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      iterating over a ``QuerySet`` will take advantage of your database to
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      load data and instantiate objects only as you need them.
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Limiting QuerySets
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------------------
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Use Python's array-slicing syntax to limit your ``QuerySet`` to a certain
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number of results. This is the equivalent of SQL's ``LIMIT`` and ``OFFSET``
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clauses.
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For example, this returns the first 5 objects (``LIMIT 5``)::
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    Entry.objects.all()[:5]
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This returns the fifth through tenth objects (``OFFSET 5 LIMIT 5``)::
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    Entry.objects.all()[5:10]
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Generally, slicing a ``QuerySet`` returns a new ``QuerySet`` -- it doesn't
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evaluate the query. An exception is if you use the "step" parameter of Python
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slice syntax. For example, this would actually execute the query in order to
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return a list of every *second* object of the first 10::
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    Entry.objects.all()[:10:2]
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To retrieve a *single* object rather than a list
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(e.g. ``SELECT foo FROM bar LIMIT 1``), use a simple index instead of a
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slice. For example, this returns the first ``Entry`` in the database, after
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ordering entries alphabetically by headline::
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    Entry.objects.order_by('headline')[0]
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This is roughly equivalent to::
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    Entry.objects.order_by('headline')[0:1].get()
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Note, however, that the first of these will raise ``IndexError`` while the
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second will raise ``DoesNotExist`` if no objects match the given criteria.
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QuerySet methods that return new QuerySets
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------------------------------------------
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Django provides a range of ``QuerySet`` refinement methods that modify either
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the types of results returned by the ``QuerySet`` or the way its SQL query is
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executed.
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``filter(**kwargs)``
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~~~~~~~~~~~~~~~~~~~~
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Returns a new ``QuerySet`` containing objects that match the given lookup
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parameters.
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The lookup parameters (``**kwargs``) should be in the format described in
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`Field lookups`_ below. Multiple parameters are joined via ``AND`` in the
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underlying SQL statement.
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``exclude(**kwargs)``
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~~~~~~~~~~~~~~~~~~~~~
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Returns a new ``QuerySet`` containing objects that do *not* match the given
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lookup parameters.
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The lookup parameters (``**kwargs``) should be in the format described in
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   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