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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"><span class="doc">Django installed</span></a> already. You can
tell Django is installed and which version by running the following command:</p>
<div class="highlight-console"><div class="highlight"><pre><span></span><span class="gp">$</span> python -c <span class="s2">"import django; print(django.get_version())"</span>
</pre></div>
</div>
<p>If Django is installed, you should see the version of your installation. If it
isn’t, you’ll get an error telling “No module named django”.</p>
<p>This tutorial is written for Django 1.8 and Python 3.2 or later. If the
Django version doesn’t match, you can refer to the tutorial for your version
of Django by using the version switcher at the bottom right corner of this
page, or update Django to the newest version. If you are still using Python
2.7, you will need to adjust the code samples slightly, as described in
comments.</p>
<p>See <a class="reference internal" href="../topics/install.html"><span class="doc">How to install Django</span></a> for advice on how to remove
older versions of Django and install a newer one.</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 internal" href="../internals/mailing-lists.html#django-users-mailing-list"><span class="std std-ref">django-users</span></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"><span class="xref std std-term">project</span></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, <code class="docutils literal"><span class="pre">cd</span></code> into a directory where you’d like to store your
code, then run the following command:</p>
<div class="highlight-console"><div class="highlight"><pre><span></span><span class="gp">$</span> django-admin startproject mysite
</pre></div>
</div>
<p>This will create a <code class="docutils literal"><span class="pre">mysite</span></code> directory in your current directory. If it didn’t
work, see <a class="reference internal" href="../faq/troubleshooting.html#troubleshooting-django-admin"><span class="std std-ref">Problems running django-admin</span></a>.</p>
<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
<code class="docutils literal"><span class="pre">django</span></code> (which will conflict with Django itself) or <code class="docutils literal"><span class="pre">test</span></code> (which
conflicts with a built-in Python package).</p>
</div>
<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 plain old PHP (with no use of modern frameworks),
you’re probably used to putting code under the Web server’s document root
(in a place such as <code class="docutils literal"><span class="pre">/var/www</span></code>). 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
<code class="file docutils literal"><span class="pre">/home/mycode</span></code>.</p>
</div>
<p>Let’s look at what <a class="reference internal" href="../ref/django-admin.html#django-admin-startproject"><code class="xref std std-djadmin docutils literal"><span class="pre">startproject</span></code></a> created:</p>
<div class="highlight-default"><div class="highlight"><pre><span></span><span class="n">mysite</span><span class="o">/</span>
<span class="n">manage</span><span class="o">.</span><span class="n">py</span>
<span class="n">mysite</span><span class="o">/</span>
<span class="n">__init__</span><span class="o">.</span><span class="n">py</span>
<span class="n">settings</span><span class="o">.</span><span class="n">py</span>
<span class="n">urls</span><span class="o">.</span><span class="n">py</span>
<span class="n">wsgi</span><span class="o">.</span><span class="n">py</span>
</pre></div>
</div>
<p>These files are:</p>
<ul class="simple">
<li>The outer <code class="file docutils literal"><span class="pre">mysite/</span></code> root 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><code class="file docutils literal"><span class="pre">manage.py</span></code>: A command-line utility that lets you interact with this
Django project in various ways. You can read all the details about
<code class="file docutils literal"><span class="pre">manage.py</span></code> in <a class="reference internal" href="../ref/django-admin.html"><span class="doc">django-admin and manage.py</span></a>.</li>
<li>The inner <code class="file docutils literal"><span class="pre">mysite/</span></code> 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. <code class="docutils literal"><span class="pre">mysite.urls</span></code>).</li>
<li><code class="file docutils literal"><span class="pre">mysite/__init__.py</span></code>: An empty file that tells Python that this
directory should be considered a Python package. (Read <a class="reference external" href="https://docs.python.org/tutorial/modules.html#packages">more about
packages</a> in the official Python docs if you’re a Python beginner.)</li>
<li><code class="file docutils literal"><span class="pre">mysite/settings.py</span></code>: Settings/configuration for this Django
project. <a class="reference internal" href="../topics/settings.html"><span class="doc">Django settings</span></a> will tell you all about how settings
work.</li>
<li><code class="file docutils literal"><span class="pre">mysite/urls.py</span></code>: 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"><span class="doc">URL dispatcher</span></a>.</li>
<li><code class="file docutils literal"><span class="pre">mysite/wsgi.py</span></code>: An entry-point for WSGI-compatible web servers to
serve your project. See <a class="reference internal" href="../howto/deployment/wsgi/index.html"><span class="doc">How to deploy with WSGI</span></a> for more details.</li>
</ul>
<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, open up <code class="file docutils literal"><span class="pre">mysite/settings.py</span></code>. It’s a normal Python module with
module-level variables representing Django settings.</p>
<p>By default, the configuration uses SQLite. If you’re new to databases, or
you’re just interested in trying Django, this is the easiest choice. SQLite is
included in Python, so you won’t need to install anything else to support your
database. When starting your first real project, however, you may want to use a
more robust database like PostgreSQL, to avoid database-switching headaches
down the road.</p>
<p>If you wish to use another database, install the appropriate <a class="reference internal" href="../topics/install.html#database-installation"><span class="std std-ref">database
bindings</span></a>, and change the following keys in the
<a class="reference internal" href="../ref/settings.html#std:setting-DATABASES"><code class="xref std std-setting docutils literal"><span class="pre">DATABASES</span></code></a> <code class="docutils literal"><span class="pre">'default'</span></code> item to match your database connection
settings:</p>
<ul class="simple">
<li><a class="reference internal" href="../ref/settings.html#std:setting-DATABASE-ENGINE"><code class="xref std std-setting docutils literal"><span class="pre">ENGINE</span></code></a> – Either
<code class="docutils literal"><span class="pre">'django.db.backends.sqlite3'</span></code>,
<code class="docutils literal"><span class="pre">'django.db.backends.postgresql_psycopg2'</span></code>,
<code class="docutils literal"><span class="pre">'django.db.backends.mysql'</span></code>, or
<code class="docutils literal"><span class="pre">'django.db.backends.oracle'</span></code>. Other backends are <a class="reference internal" href="../ref/databases.html#third-party-notes"><span class="std std-ref">also available</span></a>.</li>
<li><a class="reference internal" href="../ref/settings.html#std:setting-NAME"><code class="xref std std-setting docutils literal"><span class="pre">NAME</span></code></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"><code class="xref std std-setting docutils literal"><span class="pre">NAME</span></code></a>
should be the full absolute path, including filename, of that file. The
default value, <code class="docutils literal"><span class="pre">os.path.join(BASE_DIR,</span> <span class="pre">'db.sqlite3')</span></code>, will store the file
in your project directory.</li>
</ul>
<p>If you are not using SQLite as your database, additional settings such as <a class="reference internal" href="../ref/settings.html#std:setting-USER"><code class="xref std std-setting docutils literal"><span class="pre">USER</span></code></a>, <a class="reference internal" href="../ref/settings.html#std:setting-PASSWORD"><code class="xref std std-setting docutils literal"><span class="pre">PASSWORD</span></code></a>, <a class="reference internal" href="../ref/settings.html#std:setting-HOST"><code class="xref std std-setting docutils literal"><span class="pre">HOST</span></code></a> must be added.
For more details, see the reference documentation for <a class="reference internal" href="../ref/settings.html#std:setting-DATABASES"><code class="xref std std-setting docutils literal"><span class="pre">DATABASES</span></code></a>.</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 “<code class="docutils literal"><span class="pre">CREATE</span> <span class="pre">DATABASE</span> <span class="pre">database_name;</span></code>” 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 <code class="file docutils literal"><span class="pre">mysite/settings.py</span></code>, set <a class="reference internal" href="../ref/settings.html#std:setting-TIME_ZONE"><code class="xref std std-setting docutils literal"><span class="pre">TIME_ZONE</span></code></a> to
your time zone.</p>
<p>Also, note the <a class="reference internal" href="../ref/settings.html#std:setting-INSTALLED_APPS"><code class="xref std std-setting docutils literal"><span class="pre">INSTALLED_APPS</span></code></a> setting at the top 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"><code class="xref std std-setting docutils literal"><span class="pre">INSTALLED_APPS</span></code></a> contains the following apps, all of which
come with Django:</p>
<ul class="simple">
<li><a class="reference internal" href="../ref/contrib/admin/index.html#module-django.contrib.admin" title="django.contrib.admin: Django's admin site."><code class="xref py py-mod docutils literal"><span class="pre">django.contrib.admin</span></code></a> – The admin site. You’ll use it in <a class="reference internal" href="tutorial02.html"><span class="doc">part 2
of this tutorial</span></a>.</li>
<li><a class="reference internal" href="../topics/auth/index.html#module-django.contrib.auth" title="django.contrib.auth: Django's authentication framework."><code class="xref py py-mod docutils literal"><span class="pre">django.contrib.auth</span></code></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."><code class="xref py py-mod docutils literal"><span class="pre">django.contrib.contenttypes</span></code></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."><code class="xref py py-mod docutils literal"><span class="pre">django.contrib.sessions</span></code></a> – A session framework.</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."><code class="xref py py-mod docutils literal"><span class="pre">django.contrib.messages</span></code></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."><code class="xref py py-mod docutils literal"><span class="pre">django.contrib.staticfiles</span></code></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>Some of these applications make 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-console"><div class="highlight"><pre><span></span><span class="gp">$</span> python manage.py migrate
</pre></div>
</div>
<p>The <a class="reference internal" href="../ref/django-admin.html#django-admin-migrate"><code class="xref std std-djadmin docutils literal"><span class="pre">migrate</span></code></a> command looks at the <a class="reference internal" href="../ref/settings.html#std:setting-INSTALLED_APPS"><code class="xref std std-setting docutils literal"><span class="pre">INSTALLED_APPS</span></code></a> setting
and creates any necessary database tables according to the database settings
in your <code class="file docutils literal"><span class="pre">mysite/settings.py</span></code> file and the database migrations shipped
with the app (we’ll cover those later). You’ll see a message for each
migration it applies. If you’re interested, run the command-line client for your
database and type <code class="docutils literal"><span class="pre">\dt</span></code> (PostgreSQL), <code class="docutils literal"><span class="pre">SHOW</span> <span class="pre">TABLES;</span></code> (MySQL), <code class="docutils literal"><span class="pre">.schema</span></code>
(SQLite), or <code class="docutils literal"><span class="pre">SELECT</span> <span class="pre">TABLE_NAME</span> <span class="pre">FROM</span> <span class="pre">USER_TABLES;</span></code> (Oracle) 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"><code class="xref std std-setting docutils literal"><span class="pre">INSTALLED_APPS</span></code></a> before running <a class="reference internal" href="../ref/django-admin.html#django-admin-migrate"><code class="xref std std-djadmin docutils literal"><span class="pre">migrate</span></code></a>. The
<a class="reference internal" href="../ref/django-admin.html#django-admin-migrate"><code class="xref std std-djadmin docutils literal"><span class="pre">migrate</span></code></a> command will only run migrations for apps in
<a class="reference internal" href="../ref/settings.html#std:setting-INSTALLED_APPS"><code class="xref std std-setting docutils literal"><span class="pre">INSTALLED_APPS</span></code></a>.</p>
</div>
</div>
<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 your Django project works. Change into the outer <code class="file docutils literal"><span class="pre">mysite</span></code> directory, if
you haven’t already, and run the following commands:</p>
<div class="highlight-console"><div class="highlight"><pre><span></span><span class="gp">$</span> python manage.py runserver
</pre></div>
</div>
<p>You’ll see the following output on the command line:</p>
<pre class="literal-block">
Performing system checks...
0 errors found
March 10, 2018 - 15:50:53
Django version 1.8, using settings 'mysite.settings'
Starting development server at <a class="reference external" href="http://127.0.0.1:8000/">http://127.0.0.1:8000/</a>
Quit the server with CONTROL-C.
</pre>
<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: <strong>don’t</strong> 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"><code class="xref std std-djadmin docutils literal"><span class="pre">runserver</span></code></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-console"><div class="highlight"><pre><span></span><span class="gp">$</span> python manage.py runserver 8080
</pre></div>
</div>
<p>If you want to change the server’s IP, pass it along with the port. So to
listen on all public IPs (useful if you want to show off your work on other
computers on your network), use:</p>
<div class="highlight-console"><div class="highlight"><pre><span></span><span class="gp">$</span> 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"><code class="xref std std-djadmin docutils literal"><span class="pre">runserver</span></code></a> reference.</p>
</div>
<div class="admonition-automatic-reloading-of-djadmin-runserver admonition">
<p class="first admonition-title">Automatic reloading of <a class="reference internal" href="../ref/django-admin.html#django-admin-runserver"><code class="xref std std-djadmin docutils literal"><span class="pre">runserver</span></code></a></p>
<p class="last">The development server automatically reloads Python code for each request
as needed. You don’t need to restart the server for code changes to take
effect. However, some actions like adding files don’t trigger a restart,
so you’ll have to restart the server in these cases.</p>
</div>
</div>
</div>
<div class="section" id="s-creating-models">
<span id="s-id1"></span><span id="creating-models"></span><span id="id1"></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 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="https://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 <code class="file docutils literal"><span class="pre">manage.py</span></code> file so that it can be
imported as its own top-level module, rather than a submodule of <code class="docutils literal"><span class="pre">mysite</span></code>.</p>
<p>To create your app, make sure you’re in the same directory as <code class="file docutils literal"><span class="pre">manage.py</span></code>
and type this command:</p>
<div class="highlight-console"><div class="highlight"><pre><span></span><span class="gp">$</span> python manage.py startapp polls
</pre></div>
</div>
<p>That’ll create a directory <code class="file docutils literal"><span class="pre">polls</span></code>, which is laid out like this:</p>
<div class="highlight-default"><div class="highlight"><pre><span></span><span class="n">polls</span><span class="o">/</span>
<span class="n">__init__</span><span class="o">.</span><span class="n">py</span>
<span class="n">admin</span><span class="o">.</span><span class="n">py</span>
<span class="n">migrations</span><span class="o">/</span>
<span class="n">__init__</span><span class="o">.</span><span class="n">py</span>
<span class="n">models</span><span class="o">.</span><span class="n">py</span>
<span class="n">tests</span><span class="o">.</span><span class="n">py</span>
<span class="n">views</span><span class="o">.</span><span class="n">py</span>
</pre></div>
</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>A model is the single, definitive source of truth 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"><span class="std std-ref">DRY Principle</span></a>. The goal is to define your data model in one
place and automatically derive things from it.</p>
<p class="last">This includes the migrations - unlike in Ruby On Rails, for example, migrations
are entirely derived from your models file, and are essentially just a
history that Django can roll through to update your database schema to
match your current models.</p>
</div>
<p>In our simple poll app, we’ll create two models: <code class="docutils literal"><span class="pre">Question</span></code> and <code class="docutils literal"><span class="pre">Choice</span></code>.
A <code class="docutils literal"><span class="pre">Question</span></code> has a question and a publication date. A <code class="docutils literal"><span class="pre">Choice</span></code> has two fields:
the text of the choice and a vote tally. Each <code class="docutils literal"><span class="pre">Choice</span></code> is associated with a
<code class="docutils literal"><span class="pre">Question</span></code>.</p>
<p>These concepts are represented by simple Python classes. Edit the
<code class="file docutils literal"><span class="pre">polls/models.py</span></code> file so it looks like this:</p>
<div class="highlight-default"><div class="snippet-filename">polls/models.py</div>
<div class="highlight"><pre><span></span><span class="kn">from</span> <span class="nn">django.db</span> <span class="k">import</span> <span class="n">models</span>
<span class="k">class</span> <span class="nc">Question</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_text</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="s1">'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">question</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">Question</span><span class="p">)</span>
<span class="n">choice_text</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><span class="n">default</span><span class="o">=</span><span class="mi">0</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"><code class="xref py py-class docutils literal"><span class="pre">django.db.models.Model</span></code></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="../ref/models/fields.html#django.db.models.Field" title="django.db.models.Field"><code class="xref py py-class docutils literal"><span class="pre">Field</span></code></a>
class – e.g., <a class="reference internal" href="../ref/models/fields.html#django.db.models.CharField" title="django.db.models.CharField"><code class="xref py py-class docutils literal"><span class="pre">CharField</span></code></a> for character fields and
<a class="reference internal" href="../ref/models/fields.html#django.db.models.DateTimeField" title="django.db.models.DateTimeField"><code class="xref py py-class docutils literal"><span class="pre">DateTimeField</span></code></a> for datetimes. This tells Django what
type of data each field holds.</p>
<p>The name of each <a class="reference internal" href="../ref/models/fields.html#django.db.models.Field" title="django.db.models.Field"><code class="xref py py-class docutils literal"><span class="pre">Field</span></code></a> instance (e.g. <code class="docutils literal"><span class="pre">question_text</span></code> or
<code class="docutils literal"><span class="pre">pub_date</span></code>) 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="../ref/models/fields.html#django.db.models.Field" title="django.db.models.Field"><code class="xref py py-class docutils literal"><span class="pre">Field</span></code></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 <code class="docutils literal"><span class="pre">Question.pub_date</span></code>. 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="../ref/models/fields.html#django.db.models.Field" title="django.db.models.Field"><code class="xref py py-class docutils literal"><span class="pre">Field</span></code></a> classes have required arguments.
<a class="reference internal" href="../ref/models/fields.html#django.db.models.CharField" title="django.db.models.CharField"><code class="xref py py-class docutils literal"><span class="pre">CharField</span></code></a>, for example, requires that you give it a
<a class="reference internal" href="../ref/models/fields.html#django.db.models.CharField.max_length" title="django.db.models.CharField.max_length"><code class="xref py py-attr docutils literal"><span class="pre">max_length</span></code></a>. That’s used not only in the
database schema, but in validation, as we’ll soon see.</p>
<p>A <a class="reference internal" href="../ref/models/fields.html#django.db.models.Field" title="django.db.models.Field"><code class="xref py py-class docutils literal"><span class="pre">Field</span></code></a> can also have various optional arguments; in
this case, we’ve set the <a class="reference internal" href="../ref/models/fields.html#django.db.models.Field.default" title="django.db.models.Field.default"><code class="xref py py-attr docutils literal"><span class="pre">default</span></code></a> value of
<code class="docutils literal"><span class="pre">votes</span></code> to 0.</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"><code class="xref py py-class docutils literal"><span class="pre">ForeignKey</span></code></a>. That tells Django each <code class="docutils literal"><span class="pre">Choice</span></code> is related
to a single <code class="docutils literal"><span class="pre">Question</span></code>. Django supports all the common database relationships:
many-to-one, many-to-many and one-to-one.</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 (<code class="docutils literal"><span class="pre">CREATE</span> <span class="pre">TABLE</span></code> statements) for this app.</li>
<li>Create a Python database-access API for accessing <code class="docutils literal"><span class="pre">Question</span></code> and <code class="docutils literal"><span class="pre">Choice</span></code> objects.</li>
</ul>
<p>But first we need to tell our project that the <code class="docutils literal"><span class="pre">polls</span></code> 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 <code class="file docutils literal"><span class="pre">mysite/settings.py</span></code> file again, and change the
<a class="reference internal" href="../ref/settings.html#std:setting-INSTALLED_APPS"><code class="xref std std-setting docutils literal"><span class="pre">INSTALLED_APPS</span></code></a> setting to include the string <code class="docutils literal"><span class="pre">'polls'</span></code>. So it’ll
look like this:</p>
<div class="highlight-default"><div class="snippet-filename">mysite/settings.py</div>
<div class="highlight"><pre><span></span><span class="n">INSTALLED_APPS</span> <span class="o">=</span> <span class="p">(</span>
<span class="s1">'django.contrib.admin'</span><span class="p">,</span>
<span class="s1">'django.contrib.auth'</span><span class="p">,</span>
<span class="s1">'django.contrib.contenttypes'</span><span class="p">,</span>
<span class="s1">'django.contrib.sessions'</span><span class="p">,</span>
<span class="s1">'django.contrib.messages'</span><span class="p">,</span>
<span class="s1">'django.contrib.staticfiles'</span><span class="p">,</span>
<span class="s1">'polls'</span><span class="p">,</span>
<span class="p">)</span>
</pre></div>
</div>
<p>Now Django knows to include the <code class="docutils literal"><span class="pre">polls</span></code> app. Let’s run another command:</p>
<div class="highlight-console"><div class="highlight"><pre><span></span><span class="gp">$</span> python manage.py makemigrations polls
</pre></div>
</div>
<p>You should see something similar to the following:</p>
<div class="highlight-text"><div class="highlight"><pre><span></span>Migrations for 'polls':
0001_initial.py:
- Create model Question
- Create model Choice
- Add field question to choice
</pre></div>
</div>
<p>By running <code class="docutils literal"><span class="pre">makemigrations</span></code>, you’re telling Django that you’ve made
some changes to your models (in this case, you’ve made new ones) and that
you’d like the changes to be stored as a <em>migration</em>.</p>
<p>Migrations are how Django stores changes to your models (and thus your
database schema) - they’re just files on disk. You can read the migration
for your new model if you like; it’s the file
<code class="docutils literal"><span class="pre">polls/migrations/0001_initial.py</span></code>. Don’t worry, you’re not expected to read
them every time Django makes one, but they’re designed to be human-editable
in case you want to manually tweak how Django changes things.</p>
<p>There’s a command that will run the migrations for you and manage your database
schema automatically - that’s called <a class="reference internal" href="../ref/django-admin.html#django-admin-migrate"><code class="xref std std-djadmin docutils literal"><span class="pre">migrate</span></code></a>, and we’ll come to it in a
moment - but first, let’s see what SQL that migration would run. The
<a class="reference internal" href="../ref/django-admin.html#django-admin-sqlmigrate"><code class="xref std std-djadmin docutils literal"><span class="pre">sqlmigrate</span></code></a> command takes migration names and returns their SQL:</p>
<div class="highlight-console"><div class="highlight"><pre><span></span><span class="gp">$</span> python manage.py sqlmigrate polls 0001
</pre></div>
</div>
<p>You should see something similar to the following (we’ve reformatted it for
readability):</p>
<div class="highlight-sql"><div class="highlight"><pre><span></span><span class="k">BEGIN</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">"choice_text"</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">CREATE</span> <span class="k">TABLE</span> <span class="ss">"polls_question"</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_text"</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">ALTER</span> <span class="k">TABLE</span> <span class="ss">"polls_choice"</span> <span class="k">ADD</span> <span class="k">COLUMN</span> <span class="ss">"question_id"</span> <span class="nb">integer</span> <span class="k">NOT</span> <span class="k">NULL</span><span class="p">;</span>
<span class="k">ALTER</span> <span class="k">TABLE</span> <span class="ss">"polls_choice"</span> <span class="k">ALTER</span> <span class="k">COLUMN</span> <span class="ss">"question_id"</span> <span class="k">DROP</span> <span class="k">DEFAULT</span><span class="p">;</span>
<span class="k">CREATE</span> <span class="k">INDEX</span> <span class="ss">"polls_choice_7aa0f6ee"</span> <span class="k">ON</span> <span class="ss">"polls_choice"</span> <span class="p">(</span><span class="ss">"question_id"</span><span class="p">);</span>
<span class="k">ALTER</span> <span class="k">TABLE</span> <span class="ss">"polls_choice"</span>
<span class="k">ADD</span> <span class="k">CONSTRAINT</span> <span class="ss">"polls_choice_question_id_246c99a640fbbd72_fk_polls_question_id"</span>
<span class="k">FOREIGN</span> <span class="k">KEY</span> <span class="p">(</span><span class="ss">"question_id"</span><span class="p">)</span>
<span class="k">REFERENCES</span> <span class="ss">"polls_question"</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="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. The
example above is generated for PostgreSQL.</li>
<li>Table names are automatically generated by combining the name of the app
(<code class="docutils literal"><span class="pre">polls</span></code>) and the lowercase name of the model – <code class="docutils literal"><span class="pre">question</span></code> and
<code class="docutils literal"><span class="pre">choice</span></code>. (You can override this behavior.)</li>
<li>Primary keys (IDs) are added automatically. (You can override this, too.)</li>
<li>By convention, Django appends <code class="docutils literal"><span class="pre">"_id"</span></code> to the foreign key field name.
(Yes, you can override this, as well.)</li>
<li>The foreign key relationship is made explicit by a <code class="docutils literal"><span class="pre">FOREIGN</span> <span class="pre">KEY</span></code>
constraint. Don’t worry about the <code class="docutils literal"><span class="pre">DEFERRABLE</span></code> parts; that’s just telling
PostgreSQL to not enforce the foreign key until the end of the transaction.</li>
<li>It’s tailored to the database you’re using, so database-specific field types
such as <code class="docutils literal"><span class="pre">auto_increment</span></code> (MySQL), <code class="docutils literal"><span class="pre">serial</span></code> (PostgreSQL), or <code class="docutils literal"><span class="pre">integer</span>
<span class="pre">primary</span> <span class="pre">key</span> <span class="pre">autoincrement</span></code> (SQLite) are handled for you automatically. Same
goes for the quoting of field names – e.g., using double quotes or
single quotes.</li>
<li>The <a class="reference internal" href="../ref/django-admin.html#django-admin-sqlmigrate"><code class="xref std std-djadmin docutils literal"><span class="pre">sqlmigrate</span></code></a> command doesn’t actually run the migration on your
database - it just prints it to the screen so that you can see what SQL
Django thinks is required. It’s useful for checking what Django is going to
do or if you have database administrators who require SQL scripts for
changes.</li>
</ul>
<p>If you’re interested, you can also run
<a class="reference internal" href="../ref/django-admin.html#django-admin-check"><code class="xref std std-djadmin docutils literal"><span class="pre">python</span> <span class="pre">manage.py</span> <span class="pre">check</span></code></a>; this checks for any problems in
your project without making migrations or touching the database.</p>
<p>Now, run <a class="reference internal" href="../ref/django-admin.html#django-admin-migrate"><code class="xref std std-djadmin docutils literal"><span class="pre">migrate</span></code></a> again to create those model tables in your database:</p>
<div class="highlight-console"><div class="highlight"><pre><span></span><span class="gp">$</span> python manage.py migrate
<span class="go">Operations to perform:</span>
<span class="go"> Synchronize unmigrated apps: staticfiles, messages</span>
<span class="go"> Apply all migrations: admin, contenttypes, polls, auth, sessions</span>
<span class="go">Synchronizing apps without migrations:</span>
<span class="go"> Creating tables...</span>
<span class="go"> Running deferred SQL...</span>
<span class="go"> Installing custom SQL...</span>
<span class="go">Running migrations:</span>
<span class="go"> Rendering model states... DONE</span>
<span class="go"> Applying <migration name>... OK</span>
</pre></div>
</div>
<p>The <a class="reference internal" href="../ref/django-admin.html#django-admin-migrate"><code class="xref std std-djadmin docutils literal"><span class="pre">migrate</span></code></a> command takes all the migrations that haven’t been
applied (Django tracks which ones are applied using a special table in your
database called <code class="docutils literal"><span class="pre">django_migrations</span></code>) and runs them against your database -
essentially, synchronizing the changes you made to your models with the schema
in the database.</p>
<p>Migrations are very powerful and let you change your models over time, as you
develop your project, without the need to delete your database or tables and
make new ones - it specializes in upgrading your database live, without
losing data. We’ll cover them in more depth in a later part of the tutorial,
but for now, remember the three-step guide to making model changes:</p>
<ul class="simple">
<li>Change your models (in <code class="docutils literal"><span class="pre">models.py</span></code>).</li>
<li>Run <a class="reference internal" href="../ref/django-admin.html#django-admin-makemigrations"><code class="xref std std-djadmin docutils literal"><span class="pre">python</span> <span class="pre">manage.py</span> <span class="pre">makemigrations</span></code></a> to create
migrations for those changes</li>
<li>Run <a class="reference internal" href="../ref/django-admin.html#django-admin-migrate"><code class="xref std std-djadmin docutils literal"><span class="pre">python</span> <span class="pre">manage.py</span> <span class="pre">migrate</span></code></a> to apply those changes to
the database.</li>
</ul>
<p>The reason that there are separate commands to make and apply migrations is
because you’ll commit migrations to your version control system and ship them
with your app; they not only make your development easier, they’re also
useable by other developers and in production.</p>
<p>Read the <a class="reference internal" href="../ref/django-admin.html"><span class="doc">django-admin documentation</span></a> for full
information on what the <code class="docutils literal"><span class="pre">manage.py</span></code> 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-console"><div class="highlight"><pre><span></span><span class="gp">$</span> python manage.py shell
</pre></div>
</div>
<p>We’re using this instead of simply typing “python”, because <code class="file docutils literal"><span class="pre">manage.py</span></code>
sets the <code class="docutils literal"><span class="pre">DJANGO_SETTINGS_MODULE</span></code> environment variable, which gives Django
the Python import path to your <code class="file docutils literal"><span class="pre">mysite/settings.py</span></code> 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 <code class="file docutils literal"><span class="pre">manage.py</span></code>, no problem. Just set the
<span class="target" id="index-0"></span><a class="reference internal" href="../topics/settings.html#envvar-DJANGO_SETTINGS_MODULE"><code class="xref std std-envvar docutils literal"><span class="pre">DJANGO_SETTINGS_MODULE</span></code></a> environment variable to
<code class="docutils literal"><span class="pre">mysite.settings</span></code>, start a plain Python shell, and set up Django:</p>
<div class="highlight-pycon"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="kn">import</span> <span class="nn">django</span>
<span class="gp">>>> </span><span class="n">django</span><span class="o">.</span><span class="n">setup</span><span class="p">()</span>
</pre></div>
</div>
<p>If this raises an <code class="xref py py-exc docutils literal"><span class="pre">AttributeError</span></code>, 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>
<p>You must run <code class="docutils literal"><span class="pre">python</span></code> from the same directory <code class="file docutils literal"><span class="pre">manage.py</span></code> is in,
or ensure that directory is on the Python path, so that <code class="docutils literal"><span class="pre">import</span> <span class="pre">mysite</span></code>
works.</p>
<p class="last">For more information on all of this, see the <a class="reference internal" href="../ref/django-admin.html"><span class="doc">django-admin
documentation</span></a>.</p>
</div>
<p>Once you’re in the shell, explore the <a class="reference internal" href="../topics/db/queries.html"><span class="doc">database API</span></a>:</p>
<div class="highlight-default"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="kn">from</span> <span class="nn">polls.models</span> <span class="k">import</span> <span class="n">Question</span><span class="p">,</span> <span class="n">Choice</span> <span class="c1"># Import the model classes we just wrote.</span>
<span class="go"># No questions are in the system yet.</span>
<span class="gp">>>> </span><span class="n">Question</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 Question.</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="k">import</span> <span class="n">timezone</span>
<span class="gp">>>> </span><span class="n">q</span> <span class="o">=</span> <span class="n">Question</span><span class="p">(</span><span class="n">question_text</span><span class="o">=</span><span class="s2">"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">q</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">q</span><span class="o">.</span><span class="n">id</span>
<span class="go">1</span>
<span class="go"># Access model field values via Python attributes.</span>
<span class="gp">>>> </span><span class="n">q</span><span class="o">.</span><span class="n">question_text</span>
<span class="go">"What's new?"</span>
<span class="gp">>>> </span><span class="n">q</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">q</span><span class="o">.</span><span class="n">question_text</span> <span class="o">=</span> <span class="s2">"What's up?"</span>
<span class="gp">>>> </span><span class="n">q</span><span class="o">.</span><span class="n">save</span><span class="p">()</span>
<span class="go"># objects.all() displays all the questions in the database.</span>
<span class="gp">>>> </span><span class="n">Question</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">[<Question: Question object>]</span>
</pre></div>
</div>
<p>Wait a minute. <code class="docutils literal"><span class="pre"><Question:</span> <span class="pre">Question</span> <span class="pre">object></span></code> is, utterly, an unhelpful representation
of this object. Let’s fix that by editing the <code class="docutils literal"><span class="pre">Question</span></code> model (in the
<code class="docutils literal"><span class="pre">polls/models.py</span></code> file) and adding a
<a class="reference internal" href="../ref/models/instances.html#django.db.models.Model.__str__" title="django.db.models.Model.__str__"><code class="xref py py-meth docutils literal"><span class="pre">__str__()</span></code></a> method to both <code class="docutils literal"><span class="pre">Question</span></code> and
<code class="docutils literal"><span class="pre">Choice</span></code>:</p>
<div class="highlight-default"><div class="snippet-filename">polls/models.py</div>
<div class="highlight"><pre><span></span><span class="kn">from</span> <span class="nn">django.db</span> <span class="k">import</span> <span class="n">models</span>
<span class="k">class</span> <span class="nc">Question</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="c1"># ...</span>
<span class="k">def</span> <span class="nf">__str__</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span> <span class="c1"># __unicode__ on Python 2</span>
<span class="k">return</span> <span class="bp">self</span><span class="o">.</span><span class="n">question_text</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="c1"># ...</span>
<span class="k">def</span> <span class="nf">__str__</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span> <span class="c1"># __unicode__ on Python 2</span>
<span class="k">return</span> <span class="bp">self</span><span class="o">.</span><span class="n">choice_text</span>
</pre></div>
</div>
<p>It’s important to add <a class="reference internal" href="../ref/models/instances.html#django.db.models.Model.__str__" title="django.db.models.Model.__str__"><code class="xref py py-meth docutils literal"><span class="pre">__str__()</span></code></a> methods to your
models, not only for your own convenience when dealing with the interactive
prompt, but also because objects’ representations are used throughout Django’s
automatically-generated admin.</p>
<div class="admonition-str-or-unicode admonition">
<p class="first admonition-title"><code class="docutils literal"><span class="pre">__str__</span></code> or <code class="docutils literal"><span class="pre">__unicode__</span></code>?</p>
<p>On Python 3, it’s easy, just use
<a class="reference internal" href="../ref/models/instances.html#django.db.models.Model.__str__" title="django.db.models.Model.__str__"><code class="xref py py-meth docutils literal"><span class="pre">__str__()</span></code></a>.</p>
<p>On Python 2, you should define <a class="reference internal" href="../ref/models/instances.html#django.db.models.Model.__unicode__" title="django.db.models.Model.__unicode__"><code class="xref py py-meth docutils literal"><span class="pre">__unicode__()</span></code></a>
methods returning <code class="docutils literal"><span class="pre">unicode</span></code> values instead. 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__"><code class="xref py py-meth docutils literal"><span class="pre">__str__()</span></code></a> method that calls
<a class="reference internal" href="../ref/models/instances.html#django.db.models.Model.__unicode__" title="django.db.models.Model.__unicode__"><code class="xref py py-meth docutils literal"><span class="pre">__unicode__()</span></code></a> and converts the result to a
UTF-8 bytestring. This means that <code class="docutils literal"><span class="pre">unicode(p)</span></code> will return a Unicode
string, and <code class="docutils literal"><span class="pre">str(p)</span></code> will return a bytestring, with characters encoded
as UTF-8. Python does the opposite: <code class="docutils literal"><span class="pre">object</span></code> has a <code class="docutils literal"><span class="pre">__unicode__</span></code>
method that calls <code class="docutils literal"><span class="pre">__str__</span></code> and interprets the result as an ASCII
bytestring. This difference can create confusion.</p>
<p class="last">If all of this is gibberish to you, just use Python 3.</p>
</div>
<p>Note these are normal Python methods. Let’s add a custom method, just for
demonstration:</p>
<div class="highlight-default"><div class="snippet-filename">polls/models.py</div>
<div class="highlight"><pre><span></span><span class="kn">import</span> <span class="nn">datetime</span>
<span class="kn">from</span> <span class="nn">django.db</span> <span class="k">import</span> <span class="n">models</span>
<span class="kn">from</span> <span class="nn">django.utils</span> <span class="k">import</span> <span class="n">timezone</span>
<span class="k">class</span> <span class="nc">Question</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="c1"># ...</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 <code class="docutils literal"><span class="pre">import</span> <span class="pre">datetime</span></code> and <code class="docutils literal"><span class="pre">from</span> <span class="pre">django.utils</span> <span class="pre">import</span>
<span class="pre">timezone</span></code>, to reference Python’s standard <code class="xref py py-mod docutils literal"><span class="pre">datetime</span></code> 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."><code class="xref py py-mod docutils literal"><span class="pre">django.utils.timezone</span></code></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"><span class="doc">time zone support docs</span></a>.</p>
<p>Save these changes and start a new Python interactive shell by running
<code class="docutils literal"><span class="pre">python</span> <span class="pre">manage.py</span> <span class="pre">shell</span></code> again:</p>
<div class="highlight-default"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="kn">from</span> <span class="nn">polls.models</span> <span class="k">import</span> <span class="n">Question</span><span class="p">,</span> <span class="n">Choice</span>
<span class="go"># Make sure our __str__() addition worked.</span>
<span class="gp">>>> </span><span class="n">Question</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">[<Question: 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">Question</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">[<Question: What's up?>]</span>
<span class="gp">>>> </span><span class="n">Question</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_text__startswith</span><span class="o">=</span><span class="s1">'What'</span><span class="p">)</span>
<span class="go">[<Question: What's up?>]</span>
<span class="go"># Get the question that was published this year.</span>
<span class="gp">>>> </span><span class="kn">from</span> <span class="nn">django.utils</span> <span class="k">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">Question</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"><Question: What's up?></span>
<span class="go"># Request an ID that doesn't exist, this will raise an exception.</span>
<span class="gp">>>> </span><span class="n">Question</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">Question 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 Question.objects.get(id=1).</span>
<span class="gp">>>> </span><span class="n">Question</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"><Question: What's up?></span>
<span class="go"># Make sure our custom method worked.</span>
<span class="gp">>>> </span><span class="n">q</span> <span class="o">=</span> <span class="n">Question</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">q</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 Question 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 question's choice) which can be accessed via the API.</span>
<span class="gp">>>> </span><span class="n">q</span> <span class="o">=</span> <span class="n">Question</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">q</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">q</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_text</span><span class="o">=</span><span class="s1">'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">q</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_text</span><span class="o">=</span><span class="s1">'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">q</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_text</span><span class="o">=</span><span class="s1">'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 Question objects.</span>
<span class="gp">>>> </span><span class="n">c</span><span class="o">.</span><span class="n">question</span>
<span class="go"><Question: What's up?></span>
<span class="go"># And vice versa: Question objects get access to Choice objects.</span>
<span class="gp">>>> </span><span class="n">q</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">q</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 question 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">question__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">q</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_text__startswith</span><span class="o">=</span><span class="s1">'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"><span class="doc">Accessing related objects</span></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"><span class="std std-ref">Field lookups</span></a>. For
full details on the database API, see our <a class="reference internal" href="../topics/db/queries.html"><span class="doc">Database API reference</span></a>.</p>
<p>When you’re comfortable with the API, read <a class="reference internal" href="tutorial02.html"><span class="doc">part 2 of this tutorial</span></a> to get Django’s automatic admin working.</p>
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<h3><a href="../contents.html">Table Of Contents</a></h3>
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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="#database-setup">Database setup</a></li>
<li><a class="reference internal" href="#the-development-server">The development server</a></li>
</ul>
</li>
<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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