mirror of https://github.com/django/django.git
736 lines
28 KiB
Plaintext
736 lines
28 KiB
Plaintext
=====================================
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Writing your first Django app, part 1
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=====================================
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Let's learn by example.
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Throughout this tutorial, we'll walk you through the creation of a basic
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poll application.
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It'll consist of two parts:
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* A public site that lets people view polls and vote in them.
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* An admin site that lets you add, change and delete polls.
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We'll assume you have :doc:`Django installed </intro/install>` already. You can
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tell Django is installed and which version by running the following command:
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.. code-block:: bash
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python -c "import django; print(django.get_version())"
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If Django is installed, you should see the version of your installation. If it
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isn't, you'll get an error telling "No module named django".
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This tutorial is written for Django |version| and Python 2.x. If the Django
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version doesn't match, you can refer to the tutorial for your version of
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Django by using the version switcher at the bottom right corner of this page,
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or update Django to the newest version. If you are using Python 3.x, be aware
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that your code may need to differ from what is in the tutorial and you should
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continue using the tutorial only if you know what you are doing with Python
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3.x.
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See :doc:`How to install Django </topics/install>` for advice on how to remove
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older versions of Django and install a newer one.
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.. admonition:: Where to get help:
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If you're having trouble going through this tutorial, please post a message
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to |django-users| or drop by `#django on irc.freenode.net
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<irc://irc.freenode.net/django>`_ to chat with other Django users who might
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be able to help.
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Creating a project
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==================
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If this is your first time using Django, you'll have to take care of some
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initial setup. Namely, you'll need to auto-generate some code that establishes a
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Django :term:`project` -- a collection of settings for an instance of Django,
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including database configuration, Django-specific options and
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application-specific settings.
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From the command line, ``cd`` into a directory where you'd like to store your
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code, then run the following command:
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.. code-block:: bash
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django-admin.py startproject mysite
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This will create a ``mysite`` directory in your current directory. If it didn't
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work, see :ref:`troubleshooting-django-admin-py`.
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.. note::
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You'll need to avoid naming projects after built-in Python or Django
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components. In particular, this means you should avoid using names like
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``django`` (which will conflict with Django itself) or ``test`` (which
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conflicts with a built-in Python package).
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.. admonition:: Where should this code live?
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If your background is in plain old PHP (with no use of modern frameworks),
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you're probably used to putting code under the Web server's document root
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(in a place such as ``/var/www``). With Django, you don't do that. It's
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not a good idea to put any of this Python code within your Web server's
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document root, because it risks the possibility that people may be able
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to view your code over the Web. That's not good for security.
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Put your code in some directory **outside** of the document root, such as
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:file:`/home/mycode`.
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Let's look at what :djadmin:`startproject` created::
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mysite/
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manage.py
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mysite/
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__init__.py
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settings.py
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urls.py
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wsgi.py
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.. admonition:: Doesn't match what you see?
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The default project layout recently changed. If you're seeing a "flat"
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layout (with no inner :file:`mysite/` directory), you're probably using
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a version of Django that doesn't match this tutorial version. You'll
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want to either switch to the older tutorial or the newer Django version.
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These files are:
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* The outer :file:`mysite/` root directory is just a container for your
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project. Its name doesn't matter to Django; you can rename it to anything
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you like.
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* :file:`manage.py`: A command-line utility that lets you interact with this
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Django project in various ways. You can read all the details about
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:file:`manage.py` in :doc:`/ref/django-admin`.
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* The inner :file:`mysite/` directory is the actual Python package for your
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project. Its name is the Python package name you'll need to use to import
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anything inside it (e.g. ``mysite.urls``).
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* :file:`mysite/__init__.py`: An empty file that tells Python that this
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directory should be considered a Python package. (Read `more about
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packages`_ in the official Python docs if you're a Python beginner.)
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* :file:`mysite/settings.py`: Settings/configuration for this Django
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project. :doc:`/topics/settings` will tell you all about how settings
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work.
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* :file:`mysite/urls.py`: The URL declarations for this Django project; a
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"table of contents" of your Django-powered site. You can read more about
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URLs in :doc:`/topics/http/urls`.
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* :file:`mysite/wsgi.py`: An entry-point for WSGI-compatible web servers to
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serve your project. See :doc:`/howto/deployment/wsgi/index` for more details.
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.. _more about packages: http://docs.python.org/tutorial/modules.html#packages
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The development server
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----------------------
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Let's verify this worked. Change into the outer :file:`mysite` directory, if
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you haven't already, and run the command ``python manage.py runserver``. You'll
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see the following output on the command line:
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.. parsed-literal::
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Validating models...
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0 errors found
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|today| - 15:50:53
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Django version |version|, using settings 'mysite.settings'
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Starting development server at http://127.0.0.1:8000/
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Quit the server with CONTROL-C.
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You've started the Django development server, a lightweight Web server written
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purely in Python. We've included this with Django so you can develop things
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rapidly, without having to deal with configuring a production server -- such as
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Apache -- until you're ready for production.
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Now's a good time to note: **Don't** use this server in anything resembling a
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production environment. It's intended only for use while developing. (We're in
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the business of making Web frameworks, not Web servers.)
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Now that the server's running, visit http://127.0.0.1:8000/ with your Web
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browser. You'll see a "Welcome to Django" page, in pleasant, light-blue pastel.
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It worked!
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.. admonition:: Changing the port
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By default, the :djadmin:`runserver` command starts the development server
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on the internal IP at port 8000.
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If you want to change the server's port, pass
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it as a command-line argument. For instance, this command starts the server
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on port 8080:
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.. code-block:: bash
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$ python manage.py runserver 8080
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If you want to change the server's IP, pass it along with the port. So to
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listen on all public IPs (useful if you want to show off your work on other
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computers), use:
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.. code-block:: bash
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$ python manage.py runserver 0.0.0.0:8000
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Full docs for the development server can be found in the
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:djadmin:`runserver` reference.
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.. admonition:: Automatic reloading of :djadmin:`runserver`
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The development server automatically reloads Python code for each request
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as needed. You don't need to restart the server for code changes to take
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effect. However, some actions like adding files or compiling translation
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files don't trigger a restart, so you'll have to restart the server in
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these cases.
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Database setup
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--------------
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Now, edit :file:`mysite/settings.py`. It's a normal Python module with
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module-level variables representing Django settings.
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By default, the configuration uses SQLite. If you're new to databases, or
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you're just interested in trying Django, this is the easiest choice. SQLite is
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included in Python, so you won't need to install anything else to support your
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database.
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If you wish to use another database, install the appropriate :ref:`database
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bindings <database-installation>`, and change the following keys in the
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:setting:`DATABASES` ``'default'`` item to match your database connection
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settings:
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* :setting:`ENGINE <DATABASE-ENGINE>` -- Either
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``'django.db.backends.sqlite3'``,
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``'django.db.backends.postgresql_psycopg2'``,
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``'django.db.backends.mysql'``, or
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``'django.db.backends.oracle'``. Other backends are :setting:`also available
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<DATABASE-ENGINE>`.
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* :setting:`NAME` -- The name of your database. If you're using SQLite, the
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database will be a file on your computer; in that case, :setting:`NAME`
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should be the full absolute path, including filename, of that file. The
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default value, ``os.path.join(BASE_DIR, 'db.sqlite3')``, will store the file
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in your project directory.
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If you are not using SQLite as your database, additional settings such as :setting:`USER`, :setting:`PASSWORD`, :setting:`HOST` must be added.
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For more details, see the reference documentation for :setting:`DATABASES`.
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.. note::
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If you're using PostgreSQL or MySQL, make sure you've created a database by
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this point. Do that with "``CREATE DATABASE database_name;``" within your
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database's interactive prompt.
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If you're using SQLite, you don't need to create anything beforehand - the
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database file will be created automatically when it is needed.
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While you're editing :file:`mysite/settings.py`, set :setting:`TIME_ZONE` to
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your time zone.
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Also, note the :setting:`INSTALLED_APPS` setting at the top of the file. That
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holds the names of all Django applications that are activated in this Django
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instance. Apps can be used in multiple projects, and you can package and
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distribute them for use by others in their projects.
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By default, :setting:`INSTALLED_APPS` contains the following apps, all of which
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come with Django:
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* :mod:`django.contrib.admin` -- The admin site. You'll use it in :doc:`part 2
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of this tutorial </intro/tutorial02>`.
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* :mod:`django.contrib.auth` -- An authentication system.
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* :mod:`django.contrib.contenttypes` -- A framework for content types.
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* :mod:`django.contrib.sessions` -- A session framework.
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* :mod:`django.contrib.messages` -- A messaging framework.
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* :mod:`django.contrib.staticfiles` -- A framework for managing
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static files.
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These applications are included by default as a convenience for the common case.
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Some of these applications makes use of at least one database table, though,
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so we need to create the tables in the database before we can use them. To do
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that, run the following command:
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.. code-block:: bash
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$ python manage.py syncdb
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The :djadmin:`syncdb` command looks at the :setting:`INSTALLED_APPS` setting
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and creates any necessary database tables according to the database settings
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in your :file:`mysite/settings.py` file. You'll see a message for each
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database table it creates, and you'll get a prompt asking you if you'd like to
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create a superuser account for the authentication system. Go ahead and do
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that.
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If you're interested, run the command-line client for your database and type
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``\dt`` (PostgreSQL), ``SHOW TABLES;`` (MySQL), or ``.schema`` (SQLite) to
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display the tables Django created.
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.. admonition:: For the minimalists
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Like we said above, the default applications are included for the common
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case, but not everybody needs them. If you don't need any or all of them,
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feel free to comment-out or delete the appropriate line(s) from
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:setting:`INSTALLED_APPS` before running :djadmin:`syncdb`. The
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:djadmin:`syncdb` command will only create tables for apps in
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:setting:`INSTALLED_APPS`.
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.. _creating-models:
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Creating models
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===============
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Now that your environment -- a "project" -- is set up, you're set to start
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doing work.
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Each application you write in Django consists of a Python package that follows
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a certain convention. Django comes with a utility that automatically generates
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the basic directory structure of an app, so you can focus on writing code
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rather than creating directories.
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.. admonition:: Projects vs. apps
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What's the difference between a project and an app? An app is a Web
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application that does something -- e.g., a Weblog system, a database of
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public records or a simple poll app. A project is a collection of
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configuration and apps for a particular Web site. A project can contain
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multiple apps. An app can be in multiple projects.
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Your apps can live anywhere on your `Python path`_. In this tutorial, we'll
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create our poll app right next to your :file:`manage.py` file so that it can be
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imported as its own top-level module, rather than a submodule of ``mysite``.
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To create your app, make sure you're in the same directory as :file:`manage.py`
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and type this command:
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.. code-block:: bash
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$ python manage.py startapp polls
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That'll create a directory :file:`polls`, which is laid out like this::
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polls/
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__init__.py
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admin.py
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models.py
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tests.py
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views.py
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This directory structure will house the poll application.
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The first step in writing a database Web app in Django is to define your models
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-- essentially, your database layout, with additional metadata.
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.. admonition:: Philosophy
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A model is the single, definitive source of data about your data. It contains
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the essential fields and behaviors of the data you're storing. Django follows
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the :ref:`DRY Principle <dry>`. The goal is to define your data model in one
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place and automatically derive things from it.
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In our simple poll app, we'll create two models: ``Poll`` and ``Choice``.
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A ``Poll`` has a question and a publication date. A ``Choice`` has two fields:
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the text of the choice and a vote tally. Each ``Choice`` is associated with a
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``Poll``.
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These concepts are represented by simple Python classes. Edit the
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:file:`polls/models.py` file so it looks like this::
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from django.db import models
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class Poll(models.Model):
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question = models.CharField(max_length=200)
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pub_date = models.DateTimeField('date published')
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class Choice(models.Model):
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poll = models.ForeignKey(Poll)
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choice_text = models.CharField(max_length=200)
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votes = models.IntegerField(default=0)
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The code is straightforward. Each model is represented by a class that
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subclasses :class:`django.db.models.Model`. Each model has a number of class
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variables, each of which represents a database field in the model.
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Each field is represented by an instance of a :class:`~django.db.models.Field`
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class -- e.g., :class:`~django.db.models.CharField` for character fields and
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:class:`~django.db.models.DateTimeField` for datetimes. This tells Django what
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type of data each field holds.
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The name of each :class:`~django.db.models.Field` instance (e.g. ``question`` or
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``pub_date``) is the field's name, in machine-friendly format. You'll use this
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value in your Python code, and your database will use it as the column name.
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You can use an optional first positional argument to a
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:class:`~django.db.models.Field` to designate a human-readable name. That's used
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in a couple of introspective parts of Django, and it doubles as documentation.
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If this field isn't provided, Django will use the machine-readable name. In this
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example, we've only defined a human-readable name for ``Poll.pub_date``. For all
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other fields in this model, the field's machine-readable name will suffice as
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its human-readable name.
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Some :class:`~django.db.models.Field` classes have required arguments.
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:class:`~django.db.models.CharField`, for example, requires that you give it a
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:attr:`~django.db.models.CharField.max_length`. That's used not only in the
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database schema, but in validation, as we'll soon see.
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A :class:`~django.db.models.Field` can also have various optional arguments; in
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this case, we've set the :attr:`~django.db.models.Field.default` value of
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``votes`` to 0.
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Finally, note a relationship is defined, using
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:class:`~django.db.models.ForeignKey`. That tells Django each ``Choice`` is related
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to a single ``Poll``. Django supports all the common database relationships:
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many-to-ones, many-to-manys and one-to-ones.
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.. _`Python path`: http://docs.python.org/tutorial/modules.html#the-module-search-path
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Activating models
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=================
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That small bit of model code gives Django a lot of information. With it, Django
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is able to:
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* Create a database schema (``CREATE TABLE`` statements) for this app.
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* Create a Python database-access API for accessing ``Poll`` and ``Choice`` objects.
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But first we need to tell our project that the ``polls`` app is installed.
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.. admonition:: Philosophy
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Django apps are "pluggable": You can use an app in multiple projects, and
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you can distribute apps, because they don't have to be tied to a given
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Django installation.
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Edit the :file:`mysite/settings.py` file again, and change the
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:setting:`INSTALLED_APPS` setting to include the string ``'polls'``. So it'll
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look like this::
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INSTALLED_APPS = (
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'django.contrib.admin',
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'django.contrib.auth',
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'django.contrib.contenttypes',
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'django.contrib.sessions',
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'django.contrib.messages',
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'django.contrib.staticfiles',
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'polls',
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)
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Now Django knows to include the ``polls`` app. Let's run another command:
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.. code-block:: bash
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$ python manage.py sql polls
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You should see something similar to the following (the ``CREATE TABLE`` SQL
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statements for the polls app):
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.. code-block:: sql
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BEGIN;
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CREATE TABLE "polls_poll" (
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"id" integer NOT NULL PRIMARY KEY,
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"question" varchar(200) NOT NULL,
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"pub_date" datetime NOT NULL
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);
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CREATE TABLE "polls_choice" (
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"id" integer NOT NULL PRIMARY KEY,
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"poll_id" integer NOT NULL REFERENCES "polls_poll" ("id"),
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"choice_text" varchar(200) NOT NULL,
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"votes" integer NOT NULL
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);
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COMMIT;
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Note the following:
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* The exact output will vary depending on the database you are using. The
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example above is generated for SQLite.
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* Table names are automatically generated by combining the name of the app
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(``polls``) and the lowercase name of the model -- ``poll`` and
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``choice``. (You can override this behavior.)
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* Primary keys (IDs) are added automatically. (You can override this, too.)
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* By convention, Django appends ``"_id"`` to the foreign key field name.
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(Yes, you can override this, as well.)
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* The foreign key relationship is made explicit by a ``REFERENCES``
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statement.
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* It's tailored to the database you're using, so database-specific field
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types such as ``auto_increment`` (MySQL), ``serial`` (PostgreSQL), or
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``integer primary key`` (SQLite) are handled for you automatically. Same
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goes for quoting of field names -- e.g., using double quotes or single
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quotes.
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* The :djadmin:`sql` command doesn't actually run the SQL in your database -
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it just prints it to the screen so that you can see what SQL Django thinks
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is required. If you wanted to, you could copy and paste this SQL into your
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database prompt. However, as we will see shortly, Django provides an
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easier way of committing the SQL to the database.
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If you're interested, also run the following commands:
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* :djadmin:`python manage.py validate <validate>` -- Checks for any errors
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in the construction of your models.
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* :djadmin:`python manage.py sqlcustom polls <sqlcustom>` -- Outputs any
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:ref:`custom SQL statements <initial-sql>` (such as table modifications or
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constraints) that are defined for the application.
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* :djadmin:`python manage.py sqlclear polls <sqlclear>` -- Outputs the
|
|
necessary ``DROP TABLE`` statements for this app, according to which
|
|
tables already exist in your database (if any).
|
|
|
|
* :djadmin:`python manage.py sqlindexes polls <sqlindexes>` -- Outputs the
|
|
``CREATE INDEX`` statements for this app.
|
|
|
|
* :djadmin:`python manage.py sqlall polls <sqlall>` -- A combination of all
|
|
the SQL from the :djadmin:`sql`, :djadmin:`sqlcustom`, and
|
|
:djadmin:`sqlindexes` commands.
|
|
|
|
Looking at the output of those commands can help you understand what's actually
|
|
happening under the hood.
|
|
|
|
Now, run :djadmin:`syncdb` again to create those model tables in your database:
|
|
|
|
.. code-block:: bash
|
|
|
|
$ python manage.py syncdb
|
|
|
|
The :djadmin:`syncdb` command runs the SQL from :djadmin:`sqlall` on your
|
|
database for all apps in :setting:`INSTALLED_APPS` 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.
|
|
:djadmin:`syncdb` can be called as often as you like, and it will only ever
|
|
create the tables that don't exist.
|
|
|
|
Read the :doc:`django-admin.py documentation </ref/django-admin>` for full
|
|
information on what the ``manage.py`` utility can do.
|
|
|
|
Playing with the API
|
|
====================
|
|
|
|
Now, let's hop into the interactive Python shell and play around with the free
|
|
API Django gives you. To invoke the Python shell, use this command:
|
|
|
|
.. code-block:: bash
|
|
|
|
$ python manage.py shell
|
|
|
|
We're using this instead of simply typing "python", because :file:`manage.py`
|
|
sets the ``DJANGO_SETTINGS_MODULE`` environment variable, which gives Django
|
|
the Python import path to your :file:`mysite/settings.py` file.
|
|
|
|
.. admonition:: Bypassing manage.py
|
|
|
|
If you'd rather not use :file:`manage.py`, no problem. Just set the
|
|
``DJANGO_SETTINGS_MODULE`` environment variable to ``mysite.settings`` and
|
|
run ``python`` from the same directory :file:`manage.py` is in (or ensure
|
|
that directory is on the Python path, so that ``import mysite`` works).
|
|
|
|
For more information on all of this, see the :doc:`django-admin.py
|
|
documentation </ref/django-admin>`.
|
|
|
|
Once you're in the shell, explore the :doc:`database API </topics/db/queries>`::
|
|
|
|
>>> from polls.models import Poll, Choice # Import the model classes we just wrote.
|
|
|
|
# No polls are in the system yet.
|
|
>>> Poll.objects.all()
|
|
[]
|
|
|
|
# Create a new Poll.
|
|
# Support for time zones is enabled in the default settings file, so
|
|
# Django expects a datetime with tzinfo for pub_date. Use timezone.now()
|
|
# instead of datetime.datetime.now() and it will do the right thing.
|
|
>>> from django.utils import timezone
|
|
>>> p = Poll(question="What's new?", pub_date=timezone.now())
|
|
|
|
# Save the object into the database. You have to call save() explicitly.
|
|
>>> p.save()
|
|
|
|
# Now it has an ID. Note that this might say "1L" instead of "1", depending
|
|
# on which database you're using. That's no biggie; it just means your
|
|
# database backend prefers to return integers as Python long integer
|
|
# objects.
|
|
>>> p.id
|
|
1
|
|
|
|
# Access database columns via Python attributes.
|
|
>>> p.question
|
|
"What's new?"
|
|
>>> p.pub_date
|
|
datetime.datetime(2012, 2, 26, 13, 0, 0, 775217, tzinfo=<UTC>)
|
|
|
|
# Change values by changing the attributes, then calling save().
|
|
>>> p.question = "What's up?"
|
|
>>> p.save()
|
|
|
|
# objects.all() displays all the polls in the database.
|
|
>>> Poll.objects.all()
|
|
[<Poll: Poll object>]
|
|
|
|
|
|
Wait a minute. ``<Poll: Poll object>`` is, utterly, an unhelpful representation
|
|
of this object. Let's fix that by editing the polls model (in the
|
|
``polls/models.py`` file) and adding a
|
|
:meth:`~django.db.models.Model.__unicode__` method to both ``Poll`` and
|
|
``Choice``. On Python 3, simply replace ``__unicode__`` by ``__str__`` in the
|
|
following example::
|
|
|
|
from django.db import models
|
|
|
|
class Poll(models.Model):
|
|
# ...
|
|
def __unicode__(self): # Python 3: def __str__(self):
|
|
return self.question
|
|
|
|
class Choice(models.Model):
|
|
# ...
|
|
def __unicode__(self): # Python 3: def __str__(self):
|
|
return self.choice_text
|
|
|
|
It's important to add :meth:`~django.db.models.Model.__unicode__` methods (or
|
|
:meth:`~django.db.models.Model.__str__` on Python 3) 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.
|
|
|
|
.. admonition:: `__unicode__` or `__str__`?
|
|
|
|
On Python 3, things are simpler, just use
|
|
:meth:`~django.db.models.Model.__str__` and forget about
|
|
:meth:`~django.db.models.Model.__unicode__`.
|
|
|
|
If you're familiar with Python 2, you might be in the habit of adding
|
|
:meth:`~django.db.models.Model.__str__` methods to your classes, not
|
|
:meth:`~django.db.models.Model.__unicode__` methods. We use
|
|
:meth:`~django.db.models.Model.__unicode__` here because Django models deal
|
|
with Unicode by default. All data stored in your database is converted to
|
|
Unicode when it's returned.
|
|
|
|
Django models have a default :meth:`~django.db.models.Model.__str__` method
|
|
that calls :meth:`~django.db.models.Model.__unicode__` and converts the
|
|
result to a UTF-8 bytestring. This means that ``unicode(p)`` will return a
|
|
Unicode string, and ``str(p)`` will return a normal string, with characters
|
|
encoded as UTF-8.
|
|
|
|
If all of this is gibberish to you, just remember to add
|
|
:meth:`~django.db.models.Model.__unicode__` methods to your models. With any
|
|
luck, things should Just Work for you.
|
|
|
|
Note these are normal Python methods. Let's add a custom method, just for
|
|
demonstration::
|
|
|
|
import datetime
|
|
from django.utils import timezone
|
|
# ...
|
|
class Poll(models.Model):
|
|
# ...
|
|
def was_published_recently(self):
|
|
return self.pub_date >= timezone.now() - datetime.timedelta(days=1)
|
|
|
|
Note the addition of ``import datetime`` and ``from django.utils import
|
|
timezone``, to reference Python's standard :mod:`datetime` module and Django's
|
|
time-zone-related utilities in :mod:`django.utils.timezone`, respectively. If
|
|
you aren't familiar with time zone handling in Python, you can learn more in
|
|
the :doc:`time zone support docs </topics/i18n/timezones>`.
|
|
|
|
Save these changes and start a new Python interactive shell by running
|
|
``python manage.py shell`` again::
|
|
|
|
>>> from polls.models import Poll, Choice
|
|
|
|
# Make sure our __unicode__() addition worked.
|
|
>>> Poll.objects.all()
|
|
[<Poll: What's up?>]
|
|
|
|
# Django provides a rich database lookup API that's entirely driven by
|
|
# keyword arguments.
|
|
>>> Poll.objects.filter(id=1)
|
|
[<Poll: What's up?>]
|
|
>>> Poll.objects.filter(question__startswith='What')
|
|
[<Poll: What's up?>]
|
|
|
|
# Get the poll that was published this year.
|
|
>>> from django.utils import timezone
|
|
>>> current_year = timezone.now().year
|
|
>>> Poll.objects.get(pub_date__year=current_year)
|
|
<Poll: What's up?>
|
|
|
|
# Request an ID that doesn't exist, this will raise an exception.
|
|
>>> Poll.objects.get(id=2)
|
|
Traceback (most recent call last):
|
|
...
|
|
DoesNotExist: Poll matching query does not exist.
|
|
|
|
# Lookup by a primary key is the most common case, so Django provides a
|
|
# shortcut for primary-key exact lookups.
|
|
# The following is identical to Poll.objects.get(id=1).
|
|
>>> Poll.objects.get(pk=1)
|
|
<Poll: What's up?>
|
|
|
|
# Make sure our custom method worked.
|
|
>>> p = Poll.objects.get(pk=1)
|
|
>>> p.was_published_recently()
|
|
True
|
|
|
|
# Give the Poll a couple of Choices. The create call constructs a new
|
|
# Choice object, does the INSERT statement, adds the choice to the set
|
|
# of available choices and returns the new Choice object. Django creates
|
|
# a set to hold the "other side" of a ForeignKey relation
|
|
# (e.g. a poll's choices) which can be accessed via the API.
|
|
>>> p = Poll.objects.get(pk=1)
|
|
|
|
# Display any choices from the related object set -- none so far.
|
|
>>> p.choice_set.all()
|
|
[]
|
|
|
|
# Create three choices.
|
|
>>> p.choice_set.create(choice_text='Not much', votes=0)
|
|
<Choice: Not much>
|
|
>>> p.choice_set.create(choice_text='The sky', votes=0)
|
|
<Choice: The sky>
|
|
>>> c = p.choice_set.create(choice_text='Just hacking again', votes=0)
|
|
|
|
# Choice objects have API access to their related Poll objects.
|
|
>>> c.poll
|
|
<Poll: What's up?>
|
|
|
|
# And vice versa: Poll objects get access to Choice objects.
|
|
>>> p.choice_set.all()
|
|
[<Choice: Not much>, <Choice: The sky>, <Choice: Just hacking again>]
|
|
>>> p.choice_set.count()
|
|
3
|
|
|
|
# The API automatically follows relationships as far as you need.
|
|
# Use double underscores to separate relationships.
|
|
# This works as many levels deep as you want; there's no limit.
|
|
# Find all Choices for any poll whose pub_date is in this year
|
|
# (reusing the 'current_year' variable we created above).
|
|
>>> Choice.objects.filter(poll__pub_date__year=current_year)
|
|
[<Choice: Not much>, <Choice: The sky>, <Choice: Just hacking again>]
|
|
|
|
# Let's delete one of the choices. Use delete() for that.
|
|
>>> c = p.choice_set.filter(choice_text__startswith='Just hacking')
|
|
>>> c.delete()
|
|
|
|
For more information on model relations, see :doc:`Accessing related objects
|
|
</ref/models/relations>`. For more on how to use double underscores to perform
|
|
field lookups via the API, see :ref:`Field lookups <field-lookups-intro>`. For
|
|
full details on the database API, see our :doc:`Database API reference
|
|
</topics/db/queries>`.
|
|
|
|
When you're comfortable with the API, read :doc:`part 2 of this tutorial
|
|
</intro/tutorial02>` to get Django's automatic admin working.
|