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+=====================================
+Writing your first Django app, part 1
+=====================================
+Let's learn by example.
+Throughout this tutorial, we'll walk you through the creation of a basic
+poll application.
+It'll consist of two parts:
+* A public site that lets people view polls and vote in them.
+* An admin site that lets you add, change and delete poll.
+We'll assume you have `Django installed`_ already. You can tell Django is
+installed by running the Python interactive interpreter and typing
+``import django``. If that command runs successfully, with no errors, Django is
+installed.
+.. _`Django installed`: ../install/
+.. admonition:: Where to get help:
+If you're having trouble going through this tutorial, please post a message
+to `django-users`_ or drop by `#django`_ on ``irc.freenode.net`` and we'll
+try to help.
+.. _django-users: http://groups.google.com/group/django-users
+.. _#django: irc://irc.freenode.net/django
+Creating a project
+==================
+If this is your first time using Django, you'll have to take care of some
+initial setup. Namely, you'll need to auto-generate some code that establishes
+a Django *project* -- a collection of settings for an instance of Django,
+including database configuration, Django-specific options and
+application-specific settings.
+From the command line, ``cd`` into a directory where you'd like to store your
+code, then run the command ``django-admin.py startproject mysite``. This
+will create a ``mysite`` directory in your current directory.
+.. note::
+You'll need to avoid naming projects after built-in Python or Django
+components. In particular, this means you should avoid using names like
+``django`` (which will conflict with Django itself) or ``site`` (which
+conflicts with a built-in Python package).
+(``django-admin.py`` should be on your system path if you installed Django via
+``python setup.py``. If it's not on your path, you can find it in
+``site-packages/django/bin``, where ``site-packages`` is a directory within
+your Python installation. Consider symlinking to ``django-admin.py`` from some
+place on your path, such as ``/usr/local/bin``.)
+.. admonition:: Where should this code live?
+If your background is in PHP, you're probably used to putting code under the
+Web server's document root (in a place such as ``/var/www``). With Django,
+you don't do that. It's not a good idea to put any of this Python code within
+your Web server's document root, because it risks the possibility that
+people may be able to view your code over the Web. That's not good for
+security.
+Put your code in some directory **outside** of the document root, such as
+``/home/mycode``.
+Let's look at what ``startproject`` created::
+mysite/
+__init__.py
+manage.py
+settings.py
+urls.py
+These files are:
+* ``__init__.py``: An empty file that tells Python that this directory
+should be considered a Python package. (Read `more about packages`_ in the
+official Python docs if you're a Python beginner.)
+* ``manage.py``: A command-line utility that lets you interact with this
+Django project in various ways.
+* ``settings.py``: Settings/configuration for this Django project.
+* ``urls.py``: The URL declarations for this Django project; a "table of
+contents" of your Django-powered site.
+.. _more about packages: http://docs.python.org/tut/node8.html#packages
+The development server
+----------------------
+Let's verify this worked. Change into the ``mysite`` directory, if you
+haven't already, and run the command ``python manage.py runserver``. You'll see
+the following output on the command line::
+Validating models...
+0 errors found.
+Django version 0.95, using settings 'mysite.settings'
+Development server is running at http://127.0.0.1:8000/
+Quit the server with CONTROL-C (Unix) or CTRL-BREAK (Windows).
+You've started the Django development server, a lightweight Web server written
+purely in Python. We've included this with Django so you can develop things
+rapidly, without having to deal with configuring a production server -- such as
+Apache -- until you're ready for production.
+Now's a good time to note: DON'T use this server in anything resembling a
+production environment. It's intended only for use while developing. (We're in
+the business of making Web frameworks, not Web servers.)
+Now that the server's running, visit http://127.0.0.1:8000/ with your Web
+browser. You'll see a "Welcome to Django" page, in pleasant, light-blue pastel.
+It worked!
+.. admonition:: Changing the port
+By default, the ``runserver`` command starts the development server on port
+8000. If you want to change the server's port, pass it as a command-line
+argument. For instance, this command starts the server on port 8080::
+python manage.py runserver 8080
+Full docs for the development server are at `django-admin documentation`_.
+.. _django-admin documentation: ../django_admin/
+Database setup
+--------------
+Now, edit ``settings.py``. It's a normal Python module with module-level
+variables representing Django settings. Change these settings to match your
+database's connection parameters:
+* ``DATABASE_ENGINE`` -- Either 'postgresql', 'mysql' or 'sqlite3'.
+More coming soon.
+* ``DATABASE_NAME`` -- The name of your database, or the full (absolute)
+path to the database file if you're using SQLite.
+* ``DATABASE_USER`` -- Your database username (not used for SQLite).
+* ``DATABASE_PASSWORD`` -- Your database password (not used for SQLite).
+* ``DATABASE_HOST`` -- The host your database is on. Leave this as an
+empty string if your database server is on the same physical machine
+(not used for SQLite).
+.. admonition:: Note
+If you're using PostgreSQL or MySQL, make sure you've created a database by
+this point. Do that with "``CREATE DATABASE database_name;``" within your
+database's interactive prompt.
+While you're editing ``settings.py``, take note of the ``INSTALLED_APPS``
+setting towards the bottom of the file. That variable holds the names of all
+Django applications that are activated in this Django instance. Apps can be
+used in multiple projects, and you can package and distribute them for use
+by others in their projects.
+By default, ``INSTALLED_APPS`` contains the following apps, all of which come
+with Django:
+* ``django.contrib.auth`` -- An authentication system.
+* ``django.contrib.contenttypes`` -- A framework for content types.
+* ``django.contrib.sessions`` -- A session framework.
+* ``django.contrib.sites`` -- A framework for managing multiple sites
+with one Django installation.
+These applications are included by default as a convenience for the common
+case.
+Each of these applications makes use of at least one database table, though,
+so we need to create the tables in the database before we can use them. To do
+that, run the following command::
+python manage.py syncdb
+The ``syncdb`` command looks at the ``INSTALLED_APPS`` setting and creates any
+necessary database tables according to the database settings in your
+``settings.py`` file. You'll see a message for each database table it creates,
+and you'll get a prompt asking you if you'd like to create a superuser account
+for the authentication system. Go ahead and do that.
+If you're interested, run the command-line client for your database and type
+``\dt`` (PostgreSQL), ``SHOW TABLES;`` (MySQL), or ``.schema`` (SQLite) to
+display the tables Django created.
+.. admonition:: For the minimalists
+Like we said above, the default applications are included for the common
+case, but not everybody needs them. If you don't need any or all of them,
+feel free to comment-out or delete the appropriate line(s) from
+``INSTALLED_APPS`` before running ``syncdb``. The ``syncdb`` command will
+only create tables for apps in ``INSTALLED_APPS``.
+Creating models
+===============
+Now that your environment -- a "project" -- is set up, you're set to start
+doing work.
+Each application you write in Django consists of a Python package, somewhere
+on your `Python path`_, that follows a certain convention. Django comes with a
+utility that automatically generates the basic directory structure of an app,
+so you can focus on writing code rather than creating directories.
+.. admonition:: Projects vs. apps
+What's the difference between a project and an app? An app is a Web
+application that does something -- e.g., a weblog system, a database of
+public records or a simple poll app. A project is a collection of
+configuration and apps for a particular Web site. A project can contain
+multiple apps. An app can be in multiple projects.
+In this tutorial, we'll create our poll app in the ``mysite`` directory,
+for simplicity. As a consequence, the app will be coupled to the project --
+that is, Python code within the poll app will refer to ``mysite.polls``.
+Later in this tutorial, we'll discuss decoupling your apps for distribution.
+To create your app, make sure you're in the ``mysite`` directory and type
+this command::
+python manage.py startapp polls
+That'll create a directory ``polls``, which is laid out like this::
+polls/
+__init__.py
+models.py
+views.py
+This directory structure will house the poll application.
+The first step in writing a database Web app in Django is to define your models
+-- essentially, your database layout, with additional metadata.
+.. admonition:: Philosophy
+A model is the single, definitive source of data about your
+data. It contains the essential fields and behaviors of the data you're
+storing. Django follows the `DRY Principle`_. The goal is to define your
+data model in one place and automatically derive things from it.
+In our simple poll app, we'll create two models: polls and choices. A poll has
+a question and a publication date. A choice has two fields: the text of the
+choice and a vote tally. Each choice is associated with a poll.
+These concepts are represented by simple Python classes. Edit the
+``polls/models.py`` file so it looks like this::
+from django.db import models
+class Poll(models.Model):
+question = models.CharField(maxlength=200)
+pub_date = models.DateTimeField('date published')
+class Choice(models.Model):
+poll = models.ForeignKey(Poll)
+choice = models.CharField(maxlength=200)
+votes = models.IntegerField()
+The code is straightforward. Each model is represented by a class that
+subclasses ``django.db.models.Model``. Each model has a number of class
+variables, each of which represents a database field in the model.
+Each field is represented by an instance of a ``models.*Field`` class -- e.g.,
+``models.CharField`` for character fields and ``models.DateTimeField`` for
+datetimes. This tells Django what type of data each field holds.
+The name of each ``models.*Field`` instance (e.g. ``question`` or ``pub_date`` )
+is the field's name, in machine-friendly format. You'll use this value in your
+Python code, and your database will use it as the column name.
+You can use an optional first positional argument to a ``Field`` to designate a
+human-readable name. That's used in a couple of introspective parts of Django,
+and it doubles as documentation. If this field isn't provided, Django will use
+the machine-readable name. In this example, we've only defined a human-readable
+name for ``Poll.pub_date``. For all other fields in this model, the field's
+machine-readable name will suffice as its human-readable name.
+Some ``Field`` classes have required elements. ``CharField``, for example,
+requires that you give it a ``maxlength``. That's used not only in the database
+schema, but in validation, as we'll soon see.
+Finally, note a relationship is defined, using ``models.ForeignKey``. That tells
+Django each Choice is related to a single Poll. Django supports all the common
+database relationships: many-to-ones, many-to-manys and one-to-ones.
+.. _`Python path`: http://docs.python.org/tut/node8.html#SECTION008110000000000000000
+.. _DRY Principle: http://c2.com/cgi/wiki?DontRepeatYourself
+Activating models
+=================
+That small bit of model code gives Django a lot of information. With it, Django
+is able to:
+* Create a database schema (``CREATE TABLE`` statements) for this app.
+* Create a Python database-access API for accessing Poll and Choice objects.
+But first we need to tell our project that the ``polls`` app is installed.
+.. admonition:: Philosophy
+Django apps are "pluggable": You can use an app in multiple projects, and
+you can distribute apps, because they don't have to be tied to a given
+Django installation.
+Edit the ``settings.py`` file again, and change the ``INSTALLED_APPS`` setting
+to include the string ``'mysite.polls'``. So it'll look like this::
+INSTALLED_APPS = (
+'django.contrib.auth',
+'django.contrib.contenttypes',
+'django.contrib.sessions',
+'django.contrib.sites',
+'mysite.polls'
+)
+Now Django knows ``mysite`` includes the ``polls`` app. Let's run another command::
+python manage.py sql polls
+You should see the following (the CREATE TABLE SQL statements for the polls app)::
+BEGIN;
+CREATE TABLE "polls_poll" (
+"id" serial NOT NULL PRIMARY KEY,
+"question" varchar(200) NOT NULL,
+"pub_date" timestamp with time zone NOT NULL
+);
+CREATE TABLE "polls_choice" (
+"id" serial NOT NULL PRIMARY KEY,
+"poll_id" integer NOT NULL REFERENCES "polls_poll" ("id"),
+"choice" varchar(200) NOT NULL,
+"votes" integer NOT NULL
+);
+COMMIT;
+Note the following:
+* Table names are automatically generated by combining the name of the app
+(``polls``) and the lowercase name of the model -- ``poll`` and
+``choice``. (You can override this behavior.)
+* Primary keys (IDs) are added automatically. (You can override this, too.)
+* By convention, Django appends ``"_id"`` to the foreign key field name.
+Yes, you can override this, as well.
+* The foreign key relationship is made explicit by a ``REFERENCES`` statement.
+* It's tailored to the database you're using, so database-specific field
+types such as ``auto_increment`` (MySQL), ``serial`` (PostgreSQL), or
+``integer primary key`` (SQLite) are handled for you automatically. Same
+goes for quoting of field names -- e.g., using double quotes or single
+quotes. The author of this tutorial runs PostgreSQL, so the example
+output is in PostgreSQL syntax.
+* The `sql` command doesn't actually run the SQL in your database - it just
+prints it to the screen so that you can see what SQL Django thinks is required.
+If you wanted to, you could copy and paste this SQL into your database prompt.
+However, as we will see shortly, Django provides an easier way of committing
+the SQL to the database.
+If you're interested, also run the following commands:
+* ``python manage.py validate polls`` -- Checks for any errors in the
+construction of your models.
+* ``python manage.py sqlinitialdata polls`` -- Outputs any initial data
+required for Django's admin framework and your models.
+* ``python manage.py sqlclear polls`` -- Outputs the necessary ``DROP
+TABLE`` statements for this app, according to which tables already exist
+in your database (if any).
+* ``python manage.py sqlindexes polls`` -- Outputs the ``CREATE INDEX``
+statements for this app.
+* ``python manage.py sqlall polls`` -- A combination of all the SQL from
+the 'sql', 'sqlinitialdata', and 'sqlindexes' commands.
+Looking at the output of those commands can help you understand what's actually
+happening under the hood.
+Now, run ``syncdb`` again to create those model tables in your database::
+python manage.py syncdb
+The ``syncdb`` command runs the sql from 'sqlall' on your database for all apps
+in ``INSTALLED_APPS`` that don't already exist in your database. This creates
+all the tables, initial data and indexes for any apps you have added to your
+project since the last time you ran syncdb. ``syncdb`` can be called as often
+as you like, and it will only ever create the tables that don't exist.
+Read the `django-admin.py documentation`_ for full information on what the
+``manage.py`` utility can do.
+.. _django-admin.py documentation: ../django_admin/
+Playing with the API
+====================
+Now, let's hop into the interactive Python shell and play around with the free
+API Django gives you. To invoke the Python shell, use this command::
+python manage.py shell
+We're using this instead of simply typing "python", because ``manage.py`` sets
+up the project's environment for you. "Setting up the environment" involves two
+things:
+* Putting ``mysite`` on ``sys.path``. For flexibility, several pieces of
+Django refer to projects in Python dotted-path notation (e.g.
+``'mysite.polls.models'``). In order for this to work, the
+``mysite`` package has to be on ``sys.path``.
+We've already seen one example of this: the ``INSTALLED_APPS`` setting is
+a list of packages in dotted-path notation.
+* Setting the ``DJANGO_SETTINGS_MODULE`` environment variable, which gives
+Django the path to your ``settings.py`` file.
+.. admonition:: Bypassing manage.py
+If you'd rather not use ``manage.py``, no problem. Just make sure
+``mysite`` is at the root level on the Python path (i.e.,
+``import mysite`` works) and set the ``DJANGO_SETTINGS_MODULE``
+environment variable to ``mysite.settings``.
+For more information on all of this, see the `django-admin.py documentation`_.
+Once you're in the shell, explore the database API::
+# Import the model classes we just wrote.
+>>> from mysite.polls.models import Poll, Choice
+# No polls are in the system yet.
+>>> Poll.objects.all()
+[]
+# Create a new Poll.
+>>> from datetime import datetime
+>>> p = Poll(question="What's up?", pub_date=datetime.now())
+# Save the object into the database. You have to call save() explicitly.
+>>> p.save()
+# Now it has an ID. Note that this might say "1L" instead of "1", depending
+# on which database you're using. That's no biggie; it just means your
+# database backend prefers to return integers as Python long integer
+# objects.
+>>> p.id
+1
+# Access database columns via Python attributes.
+>>> p.question
+"What's up?"
+>>> p.pub_date
+datetime.datetime(2005, 7, 15, 12, 00, 53)
+# Change values by changing the attributes, then calling save().
+>>> p.pub_date = datetime(2005, 4, 1, 0, 0)
+>>> p.save()
+# objects.all() displays all the polls in the database.
+>>> Poll.objects.all()
+[<Poll: Poll object>]
+Wait a minute. ``<Poll: Poll object>`` is, utterly, an unhelpful
+representation of this object. Let's fix that by editing the polls model (in
+the ``polls/models.py`` file) and adding a ``__str__()`` method to both
+``Poll`` and ``Choice``::
+class Poll(models.Model):
+# ...
+def __str__(self):
+return self.question
+class Choice(models.Model):
+# ...
+def __str__(self):
+return self.choice
+It's important to add ``__str__()`` methods to your models, not only for your
+own sanity when dealing with the interactive prompt, but also because objects'
+representations are used throughout Django's automatically-generated admin.
+Note these are normal Python methods. Let's add a custom method, just for
+demonstration::
+import datetime
+# ...
+class Poll(models.Model):
+# ...
+def was_published_today(self):
+return self.pub_date.date() == datetime.date.today()
+Note the addition of ``import datetime`` to reference Python's standard
+``datetime`` module.
+Let's jump back into the Python interactive shell by running
+``python manage.py shell`` again::
+>>> from mysite.polls.models import Poll, Choice
+# Make sure our __str__() addition worked.
+>>> Poll.objects.all()
+[<Poll: What's up?>]
+# Django provides a rich database lookup API that's entirely driven by
+# keyword arguments.
+>>> Poll.objects.filter(id=1)
+[<Poll: What's up?>]
+>>> Poll.objects.filter(question__startswith='What')
+[<Poll: What's up?>]
+# Get the poll whose year is 2005. Of course, if you're going through this
+# tutorial in another year, change as appropriate.
+>>> Poll.objects.get(pub_date__year=2005)
+<Poll: What's up?>
+>>> Poll.objects.get(id=2)
+Traceback (most recent call last):
+...
+DoesNotExist: Poll matching query does not exist.
+# Lookup by a primary key is the most common case, so Django provides a
+# shortcut for primary-key exact lookups.
+# The following is identical to Poll.objects.get(id=1).
+>>> Poll.objects.get(pk=1)
+<Poll: What's up?>
+# Make sure our custom method worked.
+>>> p = Poll.objects.get(pk=1)
+>>> p.was_published_today()
+False
+# Give the Poll a couple of Choices. The create call constructs a new
+# choice object, does the INSERT statement, adds the choice to the set
+# of available choices and returns the new Choice object.
+>>> p = Poll.objects.get(pk=1)
+>>> p.choice_set.create(choice='Not much', votes=0)
+<Choice: Not much>
+>>> p.choice_set.create(choice='The sky', votes=0)
+<Choice: The sky>
+>>> c = p.choice_set.create(choice='Just hacking again', votes=0)
+# Choice objects have API access to their related Poll objects.
+>>> c.poll
+<Poll: What's up?>
+# And vice versa: Poll objects get access to Choice objects.
+>>> p.choice_set.all()
+[<Choice: Not much>, <Choice: The sky>, <Choice: Just hacking again>]
+>>> p.choice_set.count()
+3
+# The API automatically follows relationships as far as you need.
+# Use double underscores to separate relationships.
+# This works as many levels deep as you want. There's no limit.
+# Find all Choices for any poll whose pub_date is in 2005.
+>>> Choice.objects.filter(poll__pub_date__year=2005)
+[<Choice: Not much>, <Choice: The sky>, <Choice: Just hacking again>]
+# Let's delete one of the choices. Use delete() for that.
+>>> c = p.choice_set.filter(choice__startswith='Just hacking')
+>>> c.delete()
+For full details on the database API, see our `Database API reference`_.
+When you're comfortable with the API, read `part 2 of this tutorial`_ to get
+Django's automatic admin working.
+.. _Database API reference: ../db_api/
+.. _part 2 of this tutorial: ../tutorial2/