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<div class="section" id="s-writing-your-first-django-app-part-1">
<span id="writing-your-first-django-app-part-1"></span><h1>Writing your first Django app, part 1<a class="headerlink" href="#writing-your-first-django-app-part-1" title="Permalink to this headline">¶</a></h1>
<p>Let’s learn by example.</p>
<p>Throughout this tutorial, we’ll walk you through the creation of a basic
poll application.</p>
<p>It’ll consist of two parts:</p>
<ul class="simple">
<li>A public site that lets people view polls and vote in them.</li>
<li>An admin site that lets you add, change and delete polls.</li>
</ul>
<p>We’ll assume you have <a class="reference internal" href="install.html"><em>Django installed</em></a> already. You can
tell Django is installed by running the Python interactive interpreter and
typing <tt class="docutils literal"><span class="pre">import</span> <span class="pre">django</span></tt>. If that command runs successfully, with no errors,
Django is installed.</p>
<div class="admonition-where-to-get-help admonition">
<p class="first admonition-title">Where to get help:</p>
<p class="last">If you’re having trouble going through this tutorial, please post a message
to <a class="reference external" href="http://groups.google.com/group/django-users">django-users</a> or drop by <a class="reference external" href="irc://irc.freenode.net/django">#django on irc.freenode.net</a> to chat
with other Django users who might be able to help.</p>
</div>
<div class="section" id="s-creating-a-project">
<span id="creating-a-project"></span><h2>Creating a project<a class="headerlink" href="#creating-a-project" title="Permalink to this headline">¶</a></h2>
<p>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 <a class="reference internal" href="../glossary.html#term-project"><em class="xref std std-term">project</em></a> – a collection of settings for an instance of Django,
including database configuration, Django-specific options and
application-specific settings.</p>
<p>From the command line, <tt class="docutils literal"><span class="pre">cd</span></tt> into a directory where you’d like to store your
code, then run the following command:</p>
<div class="highlight-bash"><div class="highlight"><pre>django-admin.py startproject mysite
</pre></div>
</div>
<p>This will create a <tt class="docutils literal"><span class="pre">mysite</span></tt> directory in your current directory.</p>
<div class="admonition-script-name-may-differ-in-distribution-packages admonition">
<p class="first admonition-title">Script name may differ in distribution packages</p>
<p class="last">If you installed Django using a Linux distribution’s package manager
(e.g. apt-get or yum) <tt class="docutils literal"><span class="pre">django-admin.py</span></tt> may have been renamed to
<tt class="docutils literal"><span class="pre">django-admin</span></tt>. You may continue through this documentation by omitting
<tt class="docutils literal"><span class="pre">.py</span></tt> from each command.</p>
</div>
<div class="admonition-mac-os-x-permissions admonition">
<p class="first admonition-title">Mac OS X permissions</p>
<p class="last">If you’re using Mac OS X, you may see the message “permission denied” when
you try to run <tt class="docutils literal"><span class="pre">django-admin.py</span> <span class="pre">startproject</span></tt>. This is because, on
Unix-based systems like OS X, a file must be marked as “executable” before it
can be run as a program. To do this, open Terminal.app and navigate (using
the <tt class="docutils literal"><span class="pre">cd</span></tt> command) to the directory where <a class="reference internal" href="../ref/django-admin.html"><em>django-admin.py</em></a> is installed, then run the command
<tt class="docutils literal"><span class="pre">sudo</span> <span class="pre">chmod</span> <span class="pre">+x</span> <span class="pre">django-admin.py</span></tt>.</p>
</div>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p class="last">You’ll need to avoid naming projects after built-in Python or Django
components. In particular, this means you should avoid using names like
<tt class="docutils literal"><span class="pre">django</span></tt> (which will conflict with Django itself) or <tt class="docutils literal"><span class="pre">test</span></tt> (which
conflicts with a built-in Python package).</p>
</div>
<p><a class="reference internal" href="../ref/django-admin.html"><em>django-admin.py</em></a> should be on your system path if you
installed Django via <tt class="docutils literal"><span class="pre">python</span> <span class="pre">setup.py</span></tt>. If it’s not on your path, you can find
it in <tt class="docutils literal"><span class="pre">site-packages/django/bin</span></tt>, where <tt class="docutils literal"><span class="pre">site-packages</span></tt> is a directory
within your Python installation. Consider symlinking to <a class="reference internal" href="../ref/django-admin.html"><em>django-admin.py</em></a> from some place on your path, such as
<tt class="file docutils literal"><span class="pre">/usr/local/bin</span></tt>.</p>
<div class="admonition-where-should-this-code-live admonition">
<p class="first admonition-title">Where should this code live?</p>
<p>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 <tt class="docutils literal"><span class="pre">/var/www</span></tt>). 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.</p>
<p class="last">Put your code in some directory <strong>outside</strong> of the document root, such as
<tt class="file docutils literal"><span class="pre">/home/mycode</span></tt>.</p>
</div>
<p>Let’s look at what <a class="reference internal" href="../ref/django-admin.html#django-admin-startproject"><tt class="xref std std-djadmin docutils literal"><span class="pre">startproject</span></tt></a> created:</p>
<div class="highlight-python"><pre>mysite/
manage.py
mysite/
__init__.py
settings.py
urls.py
wsgi.py</pre>
</div>
<div class="admonition-doesn-t-match-what-you-see admonition">
<p class="first admonition-title">Doesn’t match what you see?</p>
<p class="last">The default project layout recently changed. If you’re seeing a “flat”
layout (with no inner <tt class="file docutils literal"><span class="pre">mysite/</span></tt> directory), you’re probably using
a version of Django that doesn’t match this tutorial version. You’ll
want to either switch to the older tutorial or the newer Django version.</p>
</div>
<p>These files are:</p>
<ul class="simple">
<li>The outer <tt class="file docutils literal"><span class="pre">mysite/</span></tt> directory is just a container for your
project. Its name doesn’t matter to Django; you can rename it to anything
you like.</li>
<li><tt class="file docutils literal"><span class="pre">manage.py</span></tt>: A command-line utility that lets you interact with this
Django project in various ways. You can read all the details about
<tt class="file docutils literal"><span class="pre">manage.py</span></tt> in <a class="reference internal" href="../ref/django-admin.html"><em>django-admin.py and manage.py</em></a>.</li>
<li>The inner <tt class="file docutils literal"><span class="pre">mysite/</span></tt> directory is the actual Python package for your
project. Its name is the Python package name you’ll need to use to import
anything inside it (e.g. <tt class="docutils literal"><span class="pre">import</span> <span class="pre">mysite.settings</span></tt>).</li>
<li><tt class="file docutils literal"><span class="pre">mysite/__init__.py</span></tt>: An empty file that tells Python that this
directory should be considered a Python package. (Read <a class="reference external" href="http://docs.python.org/tutorial/modules.html#packages">more about
packages</a> in the official Python docs if you’re a Python beginner.)</li>
<li><tt class="file docutils literal"><span class="pre">mysite/settings.py</span></tt>: Settings/configuration for this Django
project. <a class="reference internal" href="../topics/settings.html"><em>Django settings</em></a> will tell you all about how settings
work.</li>
<li><tt class="file docutils literal"><span class="pre">mysite/urls.py</span></tt>: The URL declarations for this Django project; a
“table of contents” of your Django-powered site. You can read more about
URLs in <a class="reference internal" href="../topics/http/urls.html"><em>URL dispatcher</em></a>.</li>
<li><tt class="file docutils literal"><span class="pre">mysite/wsgi.py</span></tt>: An entry-point for WSGI-compatible webservers to
serve your project. See <a class="reference internal" href="../howto/deployment/wsgi/index.html"><em>How to deploy with WSGI</em></a> for more details.</li>
</ul>
<div class="section" id="s-the-development-server">
<span id="the-development-server"></span><h3>The development server<a class="headerlink" href="#the-development-server" title="Permalink to this headline">¶</a></h3>
<p>Let’s verify this worked. Change into the outer <tt class="file docutils literal"><span class="pre">mysite</span></tt> directory, if
you haven’t already, and run the command <tt class="docutils literal"><span class="pre">python</span> <span class="pre">manage.py</span> <span class="pre">runserver</span></tt>. You’ll
see the following output on the command line:</p>
<div class="highlight-python"><pre>Validating models...
0 errors found.
Django version 1.4, using settings 'mysite.settings'
Development server is running at http://127.0.0.1:8000/
Quit the server with CONTROL-C.</pre>
</div>
<p>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.</p>
<p>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.)</p>
<p>Now that the server’s running, visit <a class="reference external" href="http://127.0.0.1:8000/">http://127.0.0.1:8000/</a> with your Web
browser. You’ll see a “Welcome to Django” page, in pleasant, light-blue pastel.
It worked!</p>
<div class="admonition-changing-the-port admonition">
<p class="first admonition-title">Changing the port</p>
<p>By default, the <a class="reference internal" href="../ref/django-admin.html#django-admin-runserver"><tt class="xref std std-djadmin docutils literal"><span class="pre">runserver</span></tt></a> command starts the development server
on the internal IP at port 8000.</p>
<p>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:</p>
<div class="highlight-bash"><div class="highlight"><pre>python manage.py runserver 8080
</pre></div>
</div>
<p>If you want to change the server’s IP, pass it along with the port. So to
listen on all public IPs (useful if you want to show off your work on other
computers), use:</p>
<div class="highlight-bash"><div class="highlight"><pre>python manage.py runserver 0.0.0.0:8000
</pre></div>
</div>
<p class="last">Full docs for the development server can be found in the
<a class="reference internal" href="../ref/django-admin.html#django-admin-runserver"><tt class="xref std std-djadmin docutils literal"><span class="pre">runserver</span></tt></a> reference.</p>
</div>
</div>
<div class="section" id="s-database-setup">
<span id="database-setup"></span><h3>Database setup<a class="headerlink" href="#database-setup" title="Permalink to this headline">¶</a></h3>
<p>Now, edit <tt class="file docutils literal"><span class="pre">mysite/settings.py</span></tt>. It’s a normal Python module with
module-level variables representing Django settings. Change the
following keys in the <a class="reference internal" href="../ref/settings.html#std:setting-DATABASES"><tt class="xref std std-setting docutils literal"><span class="pre">DATABASES</span></tt></a> <tt class="docutils literal"><span class="pre">'default'</span></tt> item to match
your database connection settings.</p>
<ul>
<li><p class="first"><a class="reference internal" href="../ref/settings.html#std:setting-DATABASE-ENGINE"><tt class="xref std std-setting docutils literal"><span class="pre">ENGINE</span></tt></a> – Either
<tt class="docutils literal"><span class="pre">'django.db.backends.postgresql_psycopg2'</span></tt>,
<tt class="docutils literal"><span class="pre">'django.db.backends.mysql'</span></tt>, <tt class="docutils literal"><span class="pre">'django.db.backends.sqlite3'</span></tt> or
<tt class="docutils literal"><span class="pre">'django.db.backends.oracle'</span></tt>. Other backends are <a class="reference internal" href="../ref/settings.html#std:setting-DATABASE-ENGINE"><tt class="xref std std-setting docutils literal"><span class="pre">also</span> <span class="pre">available</span></tt></a>.</p>
</li>
<li><p class="first"><a class="reference internal" href="../ref/settings.html#std:setting-NAME"><tt class="xref std std-setting docutils literal"><span class="pre">NAME</span></tt></a> – The name of your database. If you’re using
SQLite, the database will be a file on your computer; in that
case, <a class="reference internal" href="../ref/settings.html#std:setting-NAME"><tt class="xref std std-setting docutils literal"><span class="pre">NAME</span></tt></a> should be the full absolute path,
including filename, of that file. If the file doesn’t exist, it
will automatically be created when you synchronize the database
for the first time (see below).</p>
<p>When specifying the path, always use forward slashes, even on
Windows (e.g. <tt class="docutils literal"><span class="pre">C:/homes/user/mysite/sqlite3.db</span></tt>).</p>
</li>
<li><p class="first"><a class="reference internal" href="../ref/settings.html#std:setting-USER"><tt class="xref std std-setting docutils literal"><span class="pre">USER</span></tt></a> – Your database username (not used for SQLite).</p>
</li>
<li><p class="first"><a class="reference internal" href="../ref/settings.html#std:setting-PASSWORD"><tt class="xref std std-setting docutils literal"><span class="pre">PASSWORD</span></tt></a> – Your database password (not used for
SQLite).</p>
</li>
<li><p class="first"><a class="reference internal" href="../ref/settings.html#std:setting-HOST"><tt class="xref std std-setting docutils literal"><span class="pre">HOST</span></tt></a> – 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).</p>
</li>
</ul>
<p>If you’re new to databases, we recommend simply using SQLite by setting
<tt class="xref std std-setting docutils literal"><span class="pre">ENGINE</span></tt> to <tt class="docutils literal"><span class="pre">'django.db.backends.sqlite3'</span></tt> and <a class="reference internal" href="../ref/settings.html#std:setting-NAME"><tt class="xref std std-setting docutils literal"><span class="pre">NAME</span></tt></a> to
the place where you’d like to store the database. SQLite is included as part
of Python 2.5 and later, so you won’t need to install anything else to support
your database.</p>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p>If you’re using PostgreSQL or MySQL, make sure you’ve created a database by
this point. Do that with “<tt class="docutils literal"><span class="pre">CREATE</span> <span class="pre">DATABASE</span> <span class="pre">database_name;</span></tt>” within your
database’s interactive prompt.</p>
<p class="last">If you’re using SQLite, you don’t need to create anything beforehand - the
database file will be created automatically when it is needed.</p>
</div>
<p>While you’re editing <tt class="file docutils literal"><span class="pre">settings.py</span></tt>, set <a class="reference internal" href="../ref/settings.html#std:setting-TIME_ZONE"><tt class="xref std std-setting docutils literal"><span class="pre">TIME_ZONE</span></tt></a> to your
time zone. The default value is the Central time zone in the U.S. (Chicago).</p>
<p>Also, note the <a class="reference internal" href="../ref/settings.html#std:setting-INSTALLED_APPS"><tt class="xref std std-setting docutils literal"><span class="pre">INSTALLED_APPS</span></tt></a> setting toward the bottom of
the file. That 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.</p>
<p>By default, <a class="reference internal" href="../ref/settings.html#std:setting-INSTALLED_APPS"><tt class="xref std std-setting docutils literal"><span class="pre">INSTALLED_APPS</span></tt></a> contains the following apps, all of which
come with Django:</p>
<ul class="simple">
<li><a class="reference internal" href="../topics/auth.html#module-django.contrib.auth" title="django.contrib.auth: Django's authentication framework."><tt class="xref py py-mod docutils literal"><span class="pre">django.contrib.auth</span></tt></a> – An authentication system.</li>
<li><a class="reference internal" href="../ref/contrib/contenttypes.html#module-django.contrib.contenttypes" title="django.contrib.contenttypes: Provides generic interface to installed models."><tt class="xref py py-mod docutils literal"><span class="pre">django.contrib.contenttypes</span></tt></a> – A framework for content types.</li>
<li><a class="reference internal" href="../topics/http/sessions.html#module-django.contrib.sessions" title="django.contrib.sessions: Provides session management for Django projects."><tt class="xref py py-mod docutils literal"><span class="pre">django.contrib.sessions</span></tt></a> – A session framework.</li>
<li><a class="reference internal" href="../ref/contrib/sites.html#module-django.contrib.sites" title="django.contrib.sites: Lets you operate multiple Web sites from the same database and Django project"><tt class="xref py py-mod docutils literal"><span class="pre">django.contrib.sites</span></tt></a> – A framework for managing multiple sites
with one Django installation.</li>
<li><a class="reference internal" href="../ref/contrib/messages.html#module-django.contrib.messages" title="django.contrib.messages: Provides cookie- and session-based temporary message storage."><tt class="xref py py-mod docutils literal"><span class="pre">django.contrib.messages</span></tt></a> – A messaging framework.</li>
<li><a class="reference internal" href="../ref/contrib/staticfiles.html#module-django.contrib.staticfiles" title="django.contrib.staticfiles: An app for handling static files."><tt class="xref py py-mod docutils literal"><span class="pre">django.contrib.staticfiles</span></tt></a> – A framework for managing
static files.</li>
</ul>
<p>These applications are included by default as a convenience for the common case.</p>
<p>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:</p>
<div class="highlight-bash"><div class="highlight"><pre>python manage.py syncdb
</pre></div>
</div>
<p>The <a class="reference internal" href="../ref/django-admin.html#django-admin-syncdb"><tt class="xref std std-djadmin docutils literal"><span class="pre">syncdb</span></tt></a> command looks at the <a class="reference internal" href="../ref/settings.html#std:setting-INSTALLED_APPS"><tt class="xref std std-setting docutils literal"><span class="pre">INSTALLED_APPS</span></tt></a> setting and
creates any necessary database tables according to the database settings in your
<tt class="file docutils literal"><span class="pre">settings.py</span></tt> 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.</p>
<p>If you’re interested, run the command-line client for your database and type
<tt class="docutils literal"><span class="pre">\dt</span></tt> (PostgreSQL), <tt class="docutils literal"><span class="pre">SHOW</span> <span class="pre">TABLES;</span></tt> (MySQL), or <tt class="docutils literal"><span class="pre">.schema</span></tt> (SQLite) to
display the tables Django created.</p>
<div class="admonition-for-the-minimalists admonition">
<p class="first admonition-title">For the minimalists</p>
<p class="last">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
<a class="reference internal" href="../ref/settings.html#std:setting-INSTALLED_APPS"><tt class="xref std std-setting docutils literal"><span class="pre">INSTALLED_APPS</span></tt></a> before running <a class="reference internal" href="../ref/django-admin.html#django-admin-syncdb"><tt class="xref std std-djadmin docutils literal"><span class="pre">syncdb</span></tt></a>. The
<a class="reference internal" href="../ref/django-admin.html#django-admin-syncdb"><tt class="xref std std-djadmin docutils literal"><span class="pre">syncdb</span></tt></a> command will only create tables for apps in
<a class="reference internal" href="../ref/settings.html#std:setting-INSTALLED_APPS"><tt class="xref std std-setting docutils literal"><span class="pre">INSTALLED_APPS</span></tt></a>.</p>
</div>
</div>
</div>
<div class="section" id="s-creating-models">
<span id="s-id3"></span><span id="creating-models"></span><span id="id3"></span><h2>Creating models<a class="headerlink" href="#creating-models" title="Permalink to this headline">¶</a></h2>
<p>Now that your environment – a “project” – is set up, you’re set to start
doing work.</p>
<p>Each application you write in Django consists of a Python package, somewhere
on your <a class="reference external" href="http://docs.python.org/tutorial/modules.html#the-module-search-path">Python path</a>, 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.</p>
<div class="admonition-projects-vs-apps admonition">
<p class="first admonition-title">Projects vs. apps</p>
<p class="last">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.</p>
</div>
<p>Your apps can live anywhere on your <a class="reference external" href="http://docs.python.org/tutorial/modules.html#the-module-search-path">Python path</a>. In this tutorial, we’ll
create our poll app right next to your <tt class="file docutils literal"><span class="pre">manage.py</span></tt> file so that it can be
imported as its own top-level module, rather than a submodule of <tt class="docutils literal"><span class="pre">mysite</span></tt>.</p>
<p>To create your app, make sure you’re in the same directory as <tt class="file docutils literal"><span class="pre">manage.py</span></tt>
and type this command:</p>
<div class="highlight-bash"><div class="highlight"><pre>python manage.py startapp polls
</pre></div>
</div>
<p>That’ll create a directory <tt class="file docutils literal"><span class="pre">polls</span></tt>, which is laid out like this:</p>
<div class="highlight-python"><pre>polls/
__init__.py
models.py
tests.py
views.py</pre>
</div>
<p>This directory structure will house the poll application.</p>
<p>The first step in writing a database Web app in Django is to define your models
– essentially, your database layout, with additional metadata.</p>
<div class="admonition-philosophy admonition">
<p class="first admonition-title">Philosophy</p>
<p class="last">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 <a class="reference internal" href="../misc/design-philosophies.html#dry"><em>DRY Principle</em></a>. The goal is to define your data model in one
place and automatically derive things from it.</p>
</div>
<p>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.</p>
<p>These concepts are represented by simple Python classes. Edit the
<tt class="file docutils literal"><span class="pre">polls/models.py</span></tt> file so it looks like this:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="kn">from</span> <span class="nn">django.db</span> <span class="kn">import</span> <span class="n">models</span>
<span class="k">class</span> <span class="nc">Poll</span><span class="p">(</span><span class="n">models</span><span class="o">.</span><span class="n">Model</span><span class="p">):</span>
<span class="n">question</span> <span class="o">=</span> <span class="n">models</span><span class="o">.</span><span class="n">CharField</span><span class="p">(</span><span class="n">max_length</span><span class="o">=</span><span class="mi">200</span><span class="p">)</span>
<span class="n">pub_date</span> <span class="o">=</span> <span class="n">models</span><span class="o">.</span><span class="n">DateTimeField</span><span class="p">(</span><span class="s">'date published'</span><span class="p">)</span>
<span class="k">class</span> <span class="nc">Choice</span><span class="p">(</span><span class="n">models</span><span class="o">.</span><span class="n">Model</span><span class="p">):</span>
<span class="n">poll</span> <span class="o">=</span> <span class="n">models</span><span class="o">.</span><span class="n">ForeignKey</span><span class="p">(</span><span class="n">Poll</span><span class="p">)</span>
<span class="n">choice</span> <span class="o">=</span> <span class="n">models</span><span class="o">.</span><span class="n">CharField</span><span class="p">(</span><span class="n">max_length</span><span class="o">=</span><span class="mi">200</span><span class="p">)</span>
<span class="n">votes</span> <span class="o">=</span> <span class="n">models</span><span class="o">.</span><span class="n">IntegerField</span><span class="p">()</span>
</pre></div>
</div>
<p>The code is straightforward. Each model is represented by a class that
subclasses <a class="reference internal" href="../ref/models/instances.html#django.db.models.Model" title="django.db.models.Model"><tt class="xref py py-class docutils literal"><span class="pre">django.db.models.Model</span></tt></a>. Each model has a number of class
variables, each of which represents a database field in the model.</p>
<p>Each field is represented by an instance of a <a class="reference internal" href="../howto/custom-model-fields.html#django.db.models.Field" title="django.db.models.Field"><tt class="xref py py-class docutils literal"><span class="pre">Field</span></tt></a>
class – e.g., <a class="reference internal" href="../ref/models/fields.html#django.db.models.CharField" title="django.db.models.CharField"><tt class="xref py py-class docutils literal"><span class="pre">CharField</span></tt></a> for character fields and
<a class="reference internal" href="../ref/models/fields.html#django.db.models.DateTimeField" title="django.db.models.DateTimeField"><tt class="xref py py-class docutils literal"><span class="pre">DateTimeField</span></tt></a> for datetimes. This tells Django what
type of data each field holds.</p>
<p>The name of each <a class="reference internal" href="../howto/custom-model-fields.html#django.db.models.Field" title="django.db.models.Field"><tt class="xref py py-class docutils literal"><span class="pre">Field</span></tt></a> instance (e.g. <tt class="docutils literal"><span class="pre">question</span></tt> or
<tt class="docutils literal"><span class="pre">pub_date</span></tt> ) 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.</p>
<p>You can use an optional first positional argument to a
<a class="reference internal" href="../howto/custom-model-fields.html#django.db.models.Field" title="django.db.models.Field"><tt class="xref py py-class docutils literal"><span class="pre">Field</span></tt></a> 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 <tt class="docutils literal"><span class="pre">Poll.pub_date</span></tt>. For all
other fields in this model, the field’s machine-readable name will suffice as
its human-readable name.</p>
<p>Some <a class="reference internal" href="../howto/custom-model-fields.html#django.db.models.Field" title="django.db.models.Field"><tt class="xref py py-class docutils literal"><span class="pre">Field</span></tt></a> classes have required elements.
<a class="reference internal" href="../ref/models/fields.html#django.db.models.CharField" title="django.db.models.CharField"><tt class="xref py py-class docutils literal"><span class="pre">CharField</span></tt></a>, for example, requires that you give it a
<tt class="xref py py-attr docutils literal"><span class="pre">max_length</span></tt>. That’s used not only in the database
schema, but in validation, as we’ll soon see.</p>
<p>Finally, note a relationship is defined, using
<a class="reference internal" href="../ref/models/fields.html#django.db.models.ForeignKey" title="django.db.models.ForeignKey"><tt class="xref py py-class docutils literal"><span class="pre">ForeignKey</span></tt></a>. 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.</p>
</div>
<div class="section" id="s-activating-models">
<span id="activating-models"></span><h2>Activating models<a class="headerlink" href="#activating-models" title="Permalink to this headline">¶</a></h2>
<p>That small bit of model code gives Django a lot of information. With it, Django
is able to:</p>
<ul class="simple">
<li>Create a database schema (<tt class="docutils literal"><span class="pre">CREATE</span> <span class="pre">TABLE</span></tt> statements) for this app.</li>
<li>Create a Python database-access API for accessing Poll and Choice objects.</li>
</ul>
<p>But first we need to tell our project that the <tt class="docutils literal"><span class="pre">polls</span></tt> app is installed.</p>
<div class="admonition-philosophy admonition">
<p class="first admonition-title">Philosophy</p>
<p class="last">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.</p>
</div>
<p>Edit the <tt class="file docutils literal"><span class="pre">settings.py</span></tt> file again, and change the
<a class="reference internal" href="../ref/settings.html#std:setting-INSTALLED_APPS"><tt class="xref std std-setting docutils literal"><span class="pre">INSTALLED_APPS</span></tt></a> setting to include the string <tt class="docutils literal"><span class="pre">'polls'</span></tt>. So
it’ll look like this:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="n">INSTALLED_APPS</span> <span class="o">=</span> <span class="p">(</span>
<span class="s">'django.contrib.auth'</span><span class="p">,</span>
<span class="s">'django.contrib.contenttypes'</span><span class="p">,</span>
<span class="s">'django.contrib.sessions'</span><span class="p">,</span>
<span class="s">'django.contrib.sites'</span><span class="p">,</span>
<span class="s">'django.contrib.messages'</span><span class="p">,</span>
<span class="s">'django.contrib.staticfiles'</span><span class="p">,</span>
<span class="c"># Uncomment the next line to enable the admin:</span>
<span class="c"># 'django.contrib.admin',</span>
<span class="c"># Uncomment the next line to enable admin documentation:</span>
<span class="c"># 'django.contrib.admindocs',</span>
<span class="s">'polls'</span><span class="p">,</span>
<span class="p">)</span>
</pre></div>
</div>
<p>Now Django knows to include the <tt class="docutils literal"><span class="pre">polls</span></tt> app. Let’s run another
command:</p>
<div class="highlight-bash"><div class="highlight"><pre>python manage.py sql polls
</pre></div>
</div>
<p>You should see something similar to the following (the <tt class="docutils literal"><span class="pre">CREATE</span> <span class="pre">TABLE</span></tt> SQL
statements for the polls app):</p>
<div class="highlight-sql"><div class="highlight"><pre><span class="k">BEGIN</span><span class="p">;</span>
<span class="k">CREATE</span> <span class="k">TABLE</span> <span class="ss">"polls_poll"</span> <span class="p">(</span>
<span class="ss">"id"</span> <span class="nb">serial</span> <span class="k">NOT</span> <span class="k">NULL</span> <span class="k">PRIMARY</span> <span class="k">KEY</span><span class="p">,</span>
<span class="ss">"question"</span> <span class="nb">varchar</span><span class="p">(</span><span class="mi">200</span><span class="p">)</span> <span class="k">NOT</span> <span class="k">NULL</span><span class="p">,</span>
<span class="ss">"pub_date"</span> <span class="k">timestamp</span> <span class="k">with</span> <span class="n">time</span> <span class="k">zone</span> <span class="k">NOT</span> <span class="k">NULL</span>
<span class="p">);</span>
<span class="k">CREATE</span> <span class="k">TABLE</span> <span class="ss">"polls_choice"</span> <span class="p">(</span>
<span class="ss">"id"</span> <span class="nb">serial</span> <span class="k">NOT</span> <span class="k">NULL</span> <span class="k">PRIMARY</span> <span class="k">KEY</span><span class="p">,</span>
<span class="ss">"poll_id"</span> <span class="nb">integer</span> <span class="k">NOT</span> <span class="k">NULL</span> <span class="k">REFERENCES</span> <span class="ss">"polls_poll"</span> <span class="p">(</span><span class="ss">"id"</span><span class="p">)</span> <span class="k">DEFERRABLE</span> <span class="k">INITIALLY</span> <span class="k">DEFERRED</span><span class="p">,</span>
<span class="ss">"choice"</span> <span class="nb">varchar</span><span class="p">(</span><span class="mi">200</span><span class="p">)</span> <span class="k">NOT</span> <span class="k">NULL</span><span class="p">,</span>
<span class="ss">"votes"</span> <span class="nb">integer</span> <span class="k">NOT</span> <span class="k">NULL</span>
<span class="p">);</span>
<span class="k">COMMIT</span><span class="p">;</span>
</pre></div>
</div>
<p>Note the following:</p>
<ul class="simple">
<li>The exact output will vary depending on the database you are using.</li>
<li>Table names are automatically generated by combining the name of the app
(<tt class="docutils literal"><span class="pre">polls</span></tt>) and the lowercase name of the model – <tt class="docutils literal"><span class="pre">poll</span></tt> and
<tt class="docutils literal"><span class="pre">choice</span></tt>. (You can override this behavior.)</li>
<li>Primary keys (IDs) are added automatically. (You can override this, too.)</li>
<li>By convention, Django appends <tt class="docutils literal"><span class="pre">"_id"</span></tt> to the foreign key field name.
(Yes, you can override this, as well.)</li>
<li>The foreign key relationship is made explicit by a <tt class="docutils literal"><span class="pre">REFERENCES</span></tt>
statement.</li>
<li>It’s tailored to the database you’re using, so database-specific field
types such as <tt class="docutils literal"><span class="pre">auto_increment</span></tt> (MySQL), <tt class="docutils literal"><span class="pre">serial</span></tt> (PostgreSQL), or
<tt class="docutils literal"><span class="pre">integer</span> <span class="pre">primary</span> <span class="pre">key</span></tt> (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.</li>
<li>The <a class="reference internal" href="../ref/django-admin.html#django-admin-sql"><tt class="xref std std-djadmin docutils literal"><span class="pre">sql</span></tt></a> 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.</li>
</ul>
<p>If you’re interested, also run the following commands:</p>
<ul class="simple">
<li><a class="reference internal" href="../ref/django-admin.html#django-admin-validate"><tt class="xref std std-djadmin docutils literal"><span class="pre">python</span> <span class="pre">manage.py</span> <span class="pre">validate</span></tt></a> – Checks for any errors
in the construction of your models.</li>
<li><a class="reference internal" href="../ref/django-admin.html#django-admin-sqlcustom"><tt class="xref std std-djadmin docutils literal"><span class="pre">python</span> <span class="pre">manage.py</span> <span class="pre">sqlcustom</span> <span class="pre">polls</span></tt></a> – Outputs any
<a class="reference internal" href="../howto/initial-data.html#initial-sql"><em>custom SQL statements</em></a> (such as table modifications or
constraints) that are defined for the application.</li>
<li><a class="reference internal" href="../ref/django-admin.html#django-admin-sqlclear"><tt class="xref std std-djadmin docutils literal"><span class="pre">python</span> <span class="pre">manage.py</span> <span class="pre">sqlclear</span> <span class="pre">polls</span></tt></a> – Outputs the
necessary <tt class="docutils literal"><span class="pre">DROP</span> <span class="pre">TABLE</span></tt> statements for this app, according to which
tables already exist in your database (if any).</li>
<li><a class="reference internal" href="../ref/django-admin.html#django-admin-sqlindexes"><tt class="xref std std-djadmin docutils literal"><span class="pre">python</span> <span class="pre">manage.py</span> <span class="pre">sqlindexes</span> <span class="pre">polls</span></tt></a> – Outputs the
<tt class="docutils literal"><span class="pre">CREATE</span> <span class="pre">INDEX</span></tt> statements for this app.</li>
<li><a class="reference internal" href="../ref/django-admin.html#django-admin-sqlall"><tt class="xref std std-djadmin docutils literal"><span class="pre">python</span> <span class="pre">manage.py</span> <span class="pre">sqlall</span> <span class="pre">polls</span></tt></a> – A combination of all
the SQL from the <a class="reference internal" href="../ref/django-admin.html#django-admin-sql"><tt class="xref std std-djadmin docutils literal"><span class="pre">sql</span></tt></a>, <a class="reference internal" href="../ref/django-admin.html#django-admin-sqlcustom"><tt class="xref std std-djadmin docutils literal"><span class="pre">sqlcustom</span></tt></a>, and
<a class="reference internal" href="../ref/django-admin.html#django-admin-sqlindexes"><tt class="xref std std-djadmin docutils literal"><span class="pre">sqlindexes</span></tt></a> commands.</li>
</ul>
<p>Looking at the output of those commands can help you understand what’s actually
happening under the hood.</p>
<p>Now, run <a class="reference internal" href="../ref/django-admin.html#django-admin-syncdb"><tt class="xref std std-djadmin docutils literal"><span class="pre">syncdb</span></tt></a> again to create those model tables in your database:</p>
<div class="highlight-bash"><div class="highlight"><pre>python manage.py syncdb
</pre></div>
</div>
<p>The <a class="reference internal" href="../ref/django-admin.html#django-admin-syncdb"><tt class="xref std std-djadmin docutils literal"><span class="pre">syncdb</span></tt></a> command runs the SQL from <a class="reference internal" href="../ref/django-admin.html#django-admin-sqlall"><tt class="xref std std-djadmin docutils literal"><span class="pre">sqlall</span></tt></a> on your
database for all apps in <a class="reference internal" href="../ref/settings.html#std:setting-INSTALLED_APPS"><tt class="xref std std-setting docutils literal"><span class="pre">INSTALLED_APPS</span></tt></a> that don’t already exist in
your database. This creates all the tables, initial data and indexes for any
apps you’ve added to your project since the last time you ran syncdb.
<a class="reference internal" href="../ref/django-admin.html#django-admin-syncdb"><tt class="xref std std-djadmin docutils literal"><span class="pre">syncdb</span></tt></a> can be called as often as you like, and it will only ever
create the tables that don’t exist.</p>
<p>Read the <a class="reference internal" href="../ref/django-admin.html"><em>django-admin.py documentation</em></a> for full
information on what the <tt class="docutils literal"><span class="pre">manage.py</span></tt> utility can do.</p>
</div>
<div class="section" id="s-playing-with-the-api">
<span id="playing-with-the-api"></span><h2>Playing with the API<a class="headerlink" href="#playing-with-the-api" title="Permalink to this headline">¶</a></h2>
<p>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:</p>
<div class="highlight-bash"><div class="highlight"><pre>python manage.py shell
</pre></div>
</div>
<p>We’re using this instead of simply typing “python”, because <tt class="file docutils literal"><span class="pre">manage.py</span></tt>
sets the <tt class="docutils literal"><span class="pre">DJANGO_SETTINGS_MODULE</span></tt> environment variable, which gives Django
the Python import path to your <tt class="file docutils literal"><span class="pre">settings.py</span></tt> file.</p>
<div class="admonition-bypassing-manage-py admonition">
<p class="first admonition-title">Bypassing manage.py</p>
<p>If you’d rather not use <tt class="file docutils literal"><span class="pre">manage.py</span></tt>, no problem. Just set the
<tt class="docutils literal"><span class="pre">DJANGO_SETTINGS_MODULE</span></tt> environment variable to <tt class="docutils literal"><span class="pre">mysite.settings</span></tt> and
run <tt class="docutils literal"><span class="pre">python</span></tt> from the same directory <tt class="file docutils literal"><span class="pre">manage.py</span></tt> is in (or ensure
that directory is on the Python path, so that <tt class="docutils literal"><span class="pre">import</span> <span class="pre">mysite</span></tt> works).</p>
<p class="last">For more information on all of this, see the <a class="reference internal" href="../ref/django-admin.html"><em>django-admin.py
documentation</em></a>.</p>
</div>
<p>Once you’re in the shell, explore the <a class="reference internal" href="../topics/db/queries.html"><em>database API</em></a>:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="kn">from</span> <span class="nn">polls.models</span> <span class="kn">import</span> <span class="n">Poll</span><span class="p">,</span> <span class="n">Choice</span> <span class="c"># Import the model classes we just wrote.</span>
<span class="go"># No polls are in the system yet.</span>
<span class="gp">>>> </span><span class="n">Poll</span><span class="o">.</span><span class="n">objects</span><span class="o">.</span><span class="n">all</span><span class="p">()</span>
<span class="go">[]</span>
<span class="go"># Create a new Poll.</span>
<span class="go"># Support for time zones is enabled in the default settings file, so</span>
<span class="go"># Django expects a datetime with tzinfo for pub_date. Use timezone.now()</span>
<span class="go"># instead of datetime.datetime.now() and it will do the right thing.</span>
<span class="gp">>>> </span><span class="kn">from</span> <span class="nn">django.utils</span> <span class="kn">import</span> <span class="n">timezone</span>
<span class="gp">>>> </span><span class="n">p</span> <span class="o">=</span> <span class="n">Poll</span><span class="p">(</span><span class="n">question</span><span class="o">=</span><span class="s">"What's new?"</span><span class="p">,</span> <span class="n">pub_date</span><span class="o">=</span><span class="n">timezone</span><span class="o">.</span><span class="n">now</span><span class="p">())</span>
<span class="go"># Save the object into the database. You have to call save() explicitly.</span>
<span class="gp">>>> </span><span class="n">p</span><span class="o">.</span><span class="n">save</span><span class="p">()</span>
<span class="go"># Now it has an ID. Note that this might say "1L" instead of "1", depending</span>
<span class="go"># on which database you're using. That's no biggie; it just means your</span>
<span class="go"># database backend prefers to return integers as Python long integer</span>
<span class="go"># objects.</span>
<span class="gp">>>> </span><span class="n">p</span><span class="o">.</span><span class="n">id</span>
<span class="go">1</span>
<span class="go"># Access database columns via Python attributes.</span>
<span class="gp">>>> </span><span class="n">p</span><span class="o">.</span><span class="n">question</span>
<span class="go">"What's new?"</span>
<span class="gp">>>> </span><span class="n">p</span><span class="o">.</span><span class="n">pub_date</span>
<span class="go">datetime.datetime(2012, 2, 26, 13, 0, 0, 775217, tzinfo=<UTC>)</span>
<span class="go"># Change values by changing the attributes, then calling save().</span>
<span class="gp">>>> </span><span class="n">p</span><span class="o">.</span><span class="n">question</span> <span class="o">=</span> <span class="s">"What's up?"</span>
<span class="gp">>>> </span><span class="n">p</span><span class="o">.</span><span class="n">save</span><span class="p">()</span>
<span class="go"># objects.all() displays all the polls in the database.</span>
<span class="gp">>>> </span><span class="n">Poll</span><span class="o">.</span><span class="n">objects</span><span class="o">.</span><span class="n">all</span><span class="p">()</span>
<span class="go">[<Poll: Poll object>]</span>
</pre></div>
</div>
<p>Wait a minute. <tt class="docutils literal"><span class="pre"><Poll:</span> <span class="pre">Poll</span> <span class="pre">object></span></tt> is, utterly, an unhelpful representation
of this object. Let’s fix that by editing the polls model (in the
<tt class="docutils literal"><span class="pre">polls/models.py</span></tt> file) and adding a
<a class="reference internal" href="../ref/models/instances.html#django.db.models.Model.__unicode__" title="django.db.models.Model.__unicode__"><tt class="xref py py-meth docutils literal"><span class="pre">__unicode__()</span></tt></a> method to both <tt class="docutils literal"><span class="pre">Poll</span></tt> and
<tt class="docutils literal"><span class="pre">Choice</span></tt>:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="k">class</span> <span class="nc">Poll</span><span class="p">(</span><span class="n">models</span><span class="o">.</span><span class="n">Model</span><span class="p">):</span>
<span class="c"># ...</span>
<span class="k">def</span> <span class="nf">__unicode__</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
<span class="k">return</span> <span class="bp">self</span><span class="o">.</span><span class="n">question</span>
<span class="k">class</span> <span class="nc">Choice</span><span class="p">(</span><span class="n">models</span><span class="o">.</span><span class="n">Model</span><span class="p">):</span>
<span class="c"># ...</span>
<span class="k">def</span> <span class="nf">__unicode__</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
<span class="k">return</span> <span class="bp">self</span><span class="o">.</span><span class="n">choice</span>
</pre></div>
</div>
<p>It’s important to add <a class="reference internal" href="../ref/models/instances.html#django.db.models.Model.__unicode__" title="django.db.models.Model.__unicode__"><tt class="xref py py-meth docutils literal"><span class="pre">__unicode__()</span></tt></a> 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.</p>
<div class="admonition-why-meth-django-db-models-model-unicode-and-not-meth-django-db-models-model-str admonition">
<p class="first admonition-title">Why <a class="reference internal" href="../ref/models/instances.html#django.db.models.Model.__unicode__" title="django.db.models.Model.__unicode__"><tt class="xref py py-meth docutils literal"><span class="pre">__unicode__()</span></tt></a> and not
<a class="reference internal" href="../ref/models/instances.html#django.db.models.Model.__str__" title="django.db.models.Model.__str__"><tt class="xref py py-meth docutils literal"><span class="pre">__str__()</span></tt></a>?</p>
<p>If you’re familiar with Python, you might be in the habit of adding
<a class="reference internal" href="../ref/models/instances.html#django.db.models.Model.__str__" title="django.db.models.Model.__str__"><tt class="xref py py-meth docutils literal"><span class="pre">__str__()</span></tt></a> methods to your classes, not
<a class="reference internal" href="../ref/models/instances.html#django.db.models.Model.__unicode__" title="django.db.models.Model.__unicode__"><tt class="xref py py-meth docutils literal"><span class="pre">__unicode__()</span></tt></a> methods. We use
<a class="reference internal" href="../ref/models/instances.html#django.db.models.Model.__unicode__" title="django.db.models.Model.__unicode__"><tt class="xref py py-meth docutils literal"><span class="pre">__unicode__()</span></tt></a> here because Django models deal
with Unicode by default. All data stored in your database is converted to
Unicode when it’s returned.</p>
<p>Django models have a default <a class="reference internal" href="../ref/models/instances.html#django.db.models.Model.__str__" title="django.db.models.Model.__str__"><tt class="xref py py-meth docutils literal"><span class="pre">__str__()</span></tt></a> method
that calls <a class="reference internal" href="../ref/models/instances.html#django.db.models.Model.__unicode__" title="django.db.models.Model.__unicode__"><tt class="xref py py-meth docutils literal"><span class="pre">__unicode__()</span></tt></a> and converts the
result to a UTF-8 bytestring. This means that <tt class="docutils literal"><span class="pre">unicode(p)</span></tt> will return a
Unicode string, and <tt class="docutils literal"><span class="pre">str(p)</span></tt> will return a normal string, with characters
encoded as UTF-8.</p>
<p class="last">If all of this is gibberish to you, just remember to add
<a class="reference internal" href="../ref/models/instances.html#django.db.models.Model.__unicode__" title="django.db.models.Model.__unicode__"><tt class="xref py py-meth docutils literal"><span class="pre">__unicode__()</span></tt></a> methods to your models. With any
luck, things should Just Work for you.</p>
</div>
<p>Note these are normal Python methods. Let’s add a custom method, just for
demonstration:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="kn">import</span> <span class="nn">datetime</span>
<span class="kn">from</span> <span class="nn">django.utils</span> <span class="kn">import</span> <span class="n">timezone</span>
<span class="c"># ...</span>
<span class="k">class</span> <span class="nc">Poll</span><span class="p">(</span><span class="n">models</span><span class="o">.</span><span class="n">Model</span><span class="p">):</span>
<span class="c"># ...</span>
<span class="k">def</span> <span class="nf">was_published_recently</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
<span class="k">return</span> <span class="bp">self</span><span class="o">.</span><span class="n">pub_date</span> <span class="o">>=</span> <span class="n">timezone</span><span class="o">.</span><span class="n">now</span><span class="p">()</span> <span class="o">-</span> <span class="n">datetime</span><span class="o">.</span><span class="n">timedelta</span><span class="p">(</span><span class="n">days</span><span class="o">=</span><span class="mi">1</span><span class="p">)</span>
</pre></div>
</div>
<p>Note the addition of <tt class="docutils literal"><span class="pre">import</span> <span class="pre">datetime</span></tt> and <tt class="docutils literal"><span class="pre">from</span> <span class="pre">django.utils</span> <span class="pre">import</span>
<span class="pre">timezone</span></tt>, to reference Python’s standard <tt class="xref py py-mod docutils literal"><span class="pre">datetime</span></tt> module and Django’s
time-zone-related utilities in <a class="reference internal" href="../ref/utils.html#module-django.utils.timezone" title="django.utils.timezone: Timezone support."><tt class="xref py py-mod docutils literal"><span class="pre">django.utils.timezone</span></tt></a>, respectively. If
you aren’t familiar with time zone handling in Python, you can learn more in
the <a class="reference internal" href="../topics/i18n/timezones.html"><em>time zone support docs</em></a>.</p>
<p>Save these changes and start a new Python interactive shell by running
<tt class="docutils literal"><span class="pre">python</span> <span class="pre">manage.py</span> <span class="pre">shell</span></tt> again:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="kn">from</span> <span class="nn">polls.models</span> <span class="kn">import</span> <span class="n">Poll</span><span class="p">,</span> <span class="n">Choice</span>
<span class="go"># Make sure our __unicode__() addition worked.</span>
<span class="gp">>>> </span><span class="n">Poll</span><span class="o">.</span><span class="n">objects</span><span class="o">.</span><span class="n">all</span><span class="p">()</span>
<span class="go">[<Poll: What's up?>]</span>
<span class="go"># Django provides a rich database lookup API that's entirely driven by</span>
<span class="go"># keyword arguments.</span>
<span class="gp">>>> </span><span class="n">Poll</span><span class="o">.</span><span class="n">objects</span><span class="o">.</span><span class="n">filter</span><span class="p">(</span><span class="nb">id</span><span class="o">=</span><span class="mi">1</span><span class="p">)</span>
<span class="go">[<Poll: What's up?>]</span>
<span class="gp">>>> </span><span class="n">Poll</span><span class="o">.</span><span class="n">objects</span><span class="o">.</span><span class="n">filter</span><span class="p">(</span><span class="n">question__startswith</span><span class="o">=</span><span class="s">'What'</span><span class="p">)</span>
<span class="go">[<Poll: What's up?>]</span>
<span class="go"># Get the poll that was published this year.</span>
<span class="gp">>>> </span><span class="kn">from</span> <span class="nn">django.utils</span> <span class="kn">import</span> <span class="n">timezone</span>
<span class="gp">>>> </span><span class="n">current_year</span> <span class="o">=</span> <span class="n">timezone</span><span class="o">.</span><span class="n">now</span><span class="p">()</span><span class="o">.</span><span class="n">year</span>
<span class="gp">>>> </span><span class="n">Poll</span><span class="o">.</span><span class="n">objects</span><span class="o">.</span><span class="n">get</span><span class="p">(</span><span class="n">pub_date__year</span><span class="o">=</span><span class="n">current_year</span><span class="p">)</span>
<span class="go"><Poll: What's up?></span>
<span class="gp">>>> </span><span class="n">Poll</span><span class="o">.</span><span class="n">objects</span><span class="o">.</span><span class="n">get</span><span class="p">(</span><span class="nb">id</span><span class="o">=</span><span class="mi">2</span><span class="p">)</span>
<span class="gt">Traceback (most recent call last):</span>
<span class="o">...</span>
<span class="gr">DoesNotExist</span>: <span class="n">Poll matching query does not exist.</span>
<span class="go"># Lookup by a primary key is the most common case, so Django provides a</span>
<span class="go"># shortcut for primary-key exact lookups.</span>
<span class="go"># The following is identical to Poll.objects.get(id=1).</span>
<span class="gp">>>> </span><span class="n">Poll</span><span class="o">.</span><span class="n">objects</span><span class="o">.</span><span class="n">get</span><span class="p">(</span><span class="n">pk</span><span class="o">=</span><span class="mi">1</span><span class="p">)</span>
<span class="go"><Poll: What's up?></span>
<span class="go"># Make sure our custom method worked.</span>
<span class="gp">>>> </span><span class="n">p</span> <span class="o">=</span> <span class="n">Poll</span><span class="o">.</span><span class="n">objects</span><span class="o">.</span><span class="n">get</span><span class="p">(</span><span class="n">pk</span><span class="o">=</span><span class="mi">1</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">p</span><span class="o">.</span><span class="n">was_published_recently</span><span class="p">()</span>
<span class="go">True</span>
<span class="go"># Give the Poll a couple of Choices. The create call constructs a new</span>
<span class="go"># choice object, does the INSERT statement, adds the choice to the set</span>
<span class="go"># of available choices and returns the new Choice object. Django creates</span>
<span class="go"># a set to hold the "other side" of a ForeignKey relation</span>
<span class="go"># (e.g. a poll's choices) which can be accessed via the API.</span>
<span class="gp">>>> </span><span class="n">p</span> <span class="o">=</span> <span class="n">Poll</span><span class="o">.</span><span class="n">objects</span><span class="o">.</span><span class="n">get</span><span class="p">(</span><span class="n">pk</span><span class="o">=</span><span class="mi">1</span><span class="p">)</span>
<span class="go"># Display any choices from the related object set -- none so far.</span>
<span class="gp">>>> </span><span class="n">p</span><span class="o">.</span><span class="n">choice_set</span><span class="o">.</span><span class="n">all</span><span class="p">()</span>
<span class="go">[]</span>
<span class="go"># Create three choices.</span>
<span class="gp">>>> </span><span class="n">p</span><span class="o">.</span><span class="n">choice_set</span><span class="o">.</span><span class="n">create</span><span class="p">(</span><span class="n">choice</span><span class="o">=</span><span class="s">'Not much'</span><span class="p">,</span> <span class="n">votes</span><span class="o">=</span><span class="mi">0</span><span class="p">)</span>
<span class="go"><Choice: Not much></span>
<span class="gp">>>> </span><span class="n">p</span><span class="o">.</span><span class="n">choice_set</span><span class="o">.</span><span class="n">create</span><span class="p">(</span><span class="n">choice</span><span class="o">=</span><span class="s">'The sky'</span><span class="p">,</span> <span class="n">votes</span><span class="o">=</span><span class="mi">0</span><span class="p">)</span>
<span class="go"><Choice: The sky></span>
<span class="gp">>>> </span><span class="n">c</span> <span class="o">=</span> <span class="n">p</span><span class="o">.</span><span class="n">choice_set</span><span class="o">.</span><span class="n">create</span><span class="p">(</span><span class="n">choice</span><span class="o">=</span><span class="s">'Just hacking again'</span><span class="p">,</span> <span class="n">votes</span><span class="o">=</span><span class="mi">0</span><span class="p">)</span>
<span class="go"># Choice objects have API access to their related Poll objects.</span>
<span class="gp">>>> </span><span class="n">c</span><span class="o">.</span><span class="n">poll</span>
<span class="go"><Poll: What's up?></span>
<span class="go"># And vice versa: Poll objects get access to Choice objects.</span>
<span class="gp">>>> </span><span class="n">p</span><span class="o">.</span><span class="n">choice_set</span><span class="o">.</span><span class="n">all</span><span class="p">()</span>
<span class="go">[<Choice: Not much>, <Choice: The sky>, <Choice: Just hacking again>]</span>
<span class="gp">>>> </span><span class="n">p</span><span class="o">.</span><span class="n">choice_set</span><span class="o">.</span><span class="n">count</span><span class="p">()</span>
<span class="go">3</span>
<span class="go"># The API automatically follows relationships as far as you need.</span>
<span class="go"># Use double underscores to separate relationships.</span>
<span class="go"># This works as many levels deep as you want; there's no limit.</span>
<span class="go"># Find all Choices for any poll whose pub_date is in this year</span>
<span class="go"># (reusing the 'current_year' variable we created above).</span>
<span class="gp">>>> </span><span class="n">Choice</span><span class="o">.</span><span class="n">objects</span><span class="o">.</span><span class="n">filter</span><span class="p">(</span><span class="n">poll__pub_date__year</span><span class="o">=</span><span class="n">current_year</span><span class="p">)</span>
<span class="go">[<Choice: Not much>, <Choice: The sky>, <Choice: Just hacking again>]</span>
<span class="go"># Let's delete one of the choices. Use delete() for that.</span>
<span class="gp">>>> </span><span class="n">c</span> <span class="o">=</span> <span class="n">p</span><span class="o">.</span><span class="n">choice_set</span><span class="o">.</span><span class="n">filter</span><span class="p">(</span><span class="n">choice__startswith</span><span class="o">=</span><span class="s">'Just hacking'</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">c</span><span class="o">.</span><span class="n">delete</span><span class="p">()</span>
</pre></div>
</div>
<p>For more information on model relations, see <a class="reference internal" href="../ref/models/relations.html"><em>Accessing related objects</em></a>. For more on how to use double underscores to perform
field lookups via the API, see <a class="reference internal" href="../topics/db/queries.html#field-lookups-intro"><em>Field lookups</em></a>. For
full details on the database API, see our <a class="reference internal" href="../topics/db/queries.html"><em>Database API reference</em></a>.</p>
<p>When you’re comfortable with the API, read <a class="reference internal" href="tutorial02.html"><em>part 2 of this tutorial</em></a> to get Django’s automatic admin working.</p>
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<li><a class="reference internal" href="#">Writing your first Django app, part 1</a><ul>
<li><a class="reference internal" href="#creating-a-project">Creating a project</a><ul>
<li><a class="reference internal" href="#the-development-server">The development server</a></li>
<li><a class="reference internal" href="#database-setup">Database setup</a></li>
</ul>
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<li><a class="reference internal" href="#creating-models">Creating models</a></li>
<li><a class="reference internal" href="#activating-models">Activating models</a></li>
<li><a class="reference internal" href="#playing-with-the-api">Playing with the API</a></li>
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