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			Plaintext
		
	
	
	
	
	
| =====================================
 | |
| Writing your first Django app, part 1
 | |
| =====================================
 | |
| 
 | |
| 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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| 
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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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| 
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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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| 
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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
 | |
| isn't, you'll get an error telling "No module named django".
 | |
| 
 | |
| This tutorial is written for Django |version| and Python 2.x. 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 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
 | |
| older versions of Django and install a newer one.
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| 
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| .. admonition:: Where to get help:
 | |
| 
 | |
|     If you're having trouble going through this tutorial, please post a message
 | |
|     to `django-users`__ or drop by `#django on irc.freenode.net`__ to chat
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|     with other Django users who might be able to help.
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| 
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| __ http://groups.google.com/group/django-users
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| __ irc://irc.freenode.net/django
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| 
 | |
| Creating a project
 | |
| ==================
 | |
| 
 | |
| 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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| 
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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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| 
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| .. code-block:: bash
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| 
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|    django-admin.py startproject mysite
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| 
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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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| 
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| .. note::
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| 
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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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| 
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| .. admonition:: Where should this code live?
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| 
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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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| 
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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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| 
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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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| 
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| .. admonition:: Doesn't match what you see?
 | |
| 
 | |
|     The default project layout recently changed. If you're seeing a "flat"
 | |
|     layout (with no inner :file:`mysite/` directory), you're probably using
 | |
|     a version of Django that doesn't match this tutorial version.  You'll
 | |
|     want to either switch to the older tutorial or the newer Django version.
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| 
 | |
| These files are:
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| 
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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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| 
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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
 | |
|   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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| 
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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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| 
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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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| 
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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
 | |
| 
 | |
| The development server
 | |
| ----------------------
 | |
| 
 | |
| 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
 | |
| see the following output on the command line:
 | |
| 
 | |
| .. parsed-literal::
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| 
 | |
|     Validating models...
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| 
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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'
 | |
|     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
 | |
| purely in Python. We've included this with Django so you can develop things
 | |
| rapidly, without having to deal with configuring a production server -- such as
 | |
| Apache -- until you're ready for production.
 | |
| 
 | |
| Now's a good time to note: **Don't** use this server in anything resembling a
 | |
| production environment. It's intended only for use while developing. (We're in
 | |
| the business of making Web frameworks, not Web servers.)
 | |
| 
 | |
| Now that the server's running, visit http://127.0.0.1:8000/ with your Web
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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
 | |
|     on the internal IP at port 8000.
 | |
| 
 | |
|     If you want to change the server's port, pass
 | |
|     it as a command-line argument. For instance, this command starts the server
 | |
|     on port 8080:
 | |
| 
 | |
|     .. code-block:: bash
 | |
| 
 | |
|         $ 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
 | |
|     listen on all public IPs (useful if you want to show off your work on other
 | |
|     computers), use:
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| 
 | |
|     .. code-block:: bash
 | |
| 
 | |
|         $ python manage.py runserver 0.0.0.0:8000
 | |
| 
 | |
|     Full docs for the development server can be found in the
 | |
|     :djadmin:`runserver` reference.
 | |
| 
 | |
| .. admonition:: Automatic reloading of :djadmin:`runserver`
 | |
| 
 | |
|     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 or compiling translation
 | |
|     files don't trigger a restart, so you'll have to restart the server in
 | |
|     these cases.
 | |
| 
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| Database setup
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| --------------
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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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| 
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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
 | |
| database.
 | |
| 
 | |
| 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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| 
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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>`.
 | |
| 
 | |
| * :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
 | |
|   in your project directory.
 | |
| 
 | |
| If you are not using SQLite as your database, additional settings such as :setting:`USER`, :setting:`PASSWORD`, :setting:`HOST` must be added.
 | |
| For more details, see the reference documentation for :setting:`DATABASES`.
 | |
| 
 | |
| .. note::
 | |
| 
 | |
|     If you're using PostgreSQL or MySQL, make sure you've created a database by
 | |
|     this point. Do that with "``CREATE DATABASE database_name;``" within your
 | |
|     database's interactive prompt.
 | |
| 
 | |
|     If you're using SQLite, you don't need to create anything beforehand - the
 | |
|     database file will be created automatically when it is needed.
 | |
| 
 | |
| While you're editing :file:`mysite/settings.py`, set :setting:`TIME_ZONE` to
 | |
| your time zone.
 | |
| 
 | |
| Also, note the :setting:`INSTALLED_APPS` 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.
 | |
| 
 | |
| By default, :setting:`INSTALLED_APPS` contains the following apps, all of which
 | |
| come with Django:
 | |
| 
 | |
| * :mod:`django.contrib.admin` -- The admin site. You'll use it in :doc:`part 2
 | |
|   of this tutorial </intro/tutorial02>`.
 | |
| 
 | |
| * :mod:`django.contrib.auth` -- An authentication system.
 | |
| 
 | |
| * :mod:`django.contrib.contenttypes` -- A framework for content types.
 | |
| 
 | |
| * :mod:`django.contrib.sessions` -- A session framework.
 | |
| 
 | |
| * :mod:`django.contrib.messages` -- A messaging framework.
 | |
| 
 | |
| * :mod:`django.contrib.staticfiles` -- A framework for managing
 | |
|   static files.
 | |
| 
 | |
| These applications are included by default as a convenience for the common case.
 | |
| 
 | |
| Some of these applications makes use of at least one database table, though,
 | |
| so we need to create the tables in the database before we can use them. To do
 | |
| that, run the following command:
 | |
| 
 | |
| .. code-block:: bash
 | |
| 
 | |
|     $ python manage.py syncdb
 | |
| 
 | |
| The :djadmin:`syncdb` command looks at the :setting:`INSTALLED_APPS` setting
 | |
| and creates any necessary database tables according to the database settings
 | |
| in your :file:`mysite/settings.py` file. You'll see a message for each
 | |
| database table it creates, and you'll get a prompt asking you if you'd like to
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| create a superuser account for the authentication system. Go ahead and do
 | |
| that.
 | |
| 
 | |
| If you're interested, run the command-line client for your database and type
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| ``\dt`` (PostgreSQL), ``SHOW TABLES;`` (MySQL), or ``.schema`` (SQLite) to
 | |
| display the tables Django created.
 | |
| 
 | |
| .. admonition:: For the minimalists
 | |
| 
 | |
|     Like we said above, the default applications are included for the common
 | |
|     case, but not everybody needs them. If you don't need any or all of them,
 | |
|     feel free to comment-out or delete the appropriate line(s) from
 | |
|     :setting:`INSTALLED_APPS` before running :djadmin:`syncdb`. The
 | |
|     :djadmin:`syncdb` command will only create tables for apps in
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|     :setting:`INSTALLED_APPS`.
 | |
| 
 | |
| .. _creating-models:
 | |
| 
 | |
| Creating models
 | |
| ===============
 | |
| 
 | |
| Now that your environment -- a "project" -- is set up, you're set to start
 | |
| doing work.
 | |
| 
 | |
| Each application you write in Django consists of a Python package that follows
 | |
| a certain convention. Django comes with a utility that automatically generates
 | |
| the basic directory structure of an app, so you can focus on writing code
 | |
| rather than creating directories.
 | |
| 
 | |
| .. admonition:: Projects vs. apps
 | |
| 
 | |
|     What's the difference between a project and an app? An app is a Web
 | |
|     application that does something -- e.g., a Weblog system, a database of
 | |
|     public records or a simple poll app. A project is a collection of
 | |
|     configuration and apps for a particular Web site. A project can contain
 | |
|     multiple apps. An app can be in multiple projects.
 | |
| 
 | |
| Your apps can live anywhere on your `Python path`_. In this tutorial, we'll
 | |
| create our poll app right next to your :file:`manage.py` file so that it can be
 | |
| imported as its own top-level module, rather than a submodule of ``mysite``.
 | |
| 
 | |
| To create your app, make sure you're in the same directory as :file:`manage.py`
 | |
| and type this command:
 | |
| 
 | |
| .. code-block:: bash
 | |
| 
 | |
|     $ python manage.py startapp polls
 | |
| 
 | |
| That'll create a directory :file:`polls`, which is laid out like this::
 | |
| 
 | |
|     polls/
 | |
|         __init__.py
 | |
|         admin.py
 | |
|         models.py
 | |
|         tests.py
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|         views.py
 | |
| 
 | |
| This directory structure will house the poll application.
 | |
| 
 | |
| The first step in writing a database Web app in Django is to define your models
 | |
| -- essentially, your database layout, with additional metadata.
 | |
| 
 | |
| .. admonition:: Philosophy
 | |
| 
 | |
|    A model is the single, definitive source of data about your data. It contains
 | |
|    the essential fields and behaviors of the data you're storing. Django follows
 | |
|    the :ref:`DRY Principle <dry>`. The goal is to define your data model in one
 | |
|    place and automatically derive things from it.
 | |
| 
 | |
| In our simple poll app, we'll create two models: ``Poll`` and ``Choice``.
 | |
| A ``Poll`` has a question and a publication date. A ``Choice`` has two fields:
 | |
| the text of the choice and a vote tally. Each ``Choice`` is associated with a
 | |
| ``Poll``.
 | |
| 
 | |
| These concepts are represented by simple Python classes. Edit the
 | |
| :file:`polls/models.py` file so it looks like this::
 | |
| 
 | |
|     from django.db import models
 | |
| 
 | |
|     class Poll(models.Model):
 | |
|         question = models.CharField(max_length=200)
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|         pub_date = models.DateTimeField('date published')
 | |
| 
 | |
|     class Choice(models.Model):
 | |
|         poll = models.ForeignKey(Poll)
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|         choice_text = models.CharField(max_length=200)
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|         votes = models.IntegerField(default=0)
 | |
| 
 | |
| The code is straightforward. Each model is represented by a class that
 | |
| subclasses :class:`django.db.models.Model`. Each model has a number of class
 | |
| variables, each of which represents a database field in the model.
 | |
| 
 | |
| Each field is represented by an instance of a :class:`~django.db.models.Field`
 | |
| class -- e.g., :class:`~django.db.models.CharField` for character fields and
 | |
| :class:`~django.db.models.DateTimeField` for datetimes. This tells Django what
 | |
| type of data each field holds.
 | |
| 
 | |
| The name of each :class:`~django.db.models.Field` instance (e.g. ``question`` or
 | |
| ``pub_date``) is the field's name, in machine-friendly format. You'll use this
 | |
| value in your Python code, and your database will use it as the column name.
 | |
| 
 | |
| You can use an optional first positional argument to a
 | |
| :class:`~django.db.models.Field` to designate a human-readable name. That's used
 | |
| in a couple of introspective parts of Django, and it doubles as documentation.
 | |
| If this field isn't provided, Django will use the machine-readable name. In this
 | |
| example, we've only defined a human-readable name for ``Poll.pub_date``. For all
 | |
| other fields in this model, the field's machine-readable name will suffice as
 | |
| its human-readable name.
 | |
| 
 | |
| Some :class:`~django.db.models.Field` classes have required arguments.
 | |
| :class:`~django.db.models.CharField`, for example, requires that you give it a
 | |
| :attr:`~django.db.models.CharField.max_length`. That's used not only in the
 | |
| database schema, but in validation, as we'll soon see.
 | |
| 
 | |
| A :class:`~django.db.models.Field` can also have various optional arguments; in
 | |
| this case, we've set the :attr:`~django.db.models.Field.default` value of
 | |
| ``votes`` to 0.
 | |
| 
 | |
| Finally, note a relationship is defined, using
 | |
| :class:`~django.db.models.ForeignKey`. That tells Django each ``Choice`` is related
 | |
| to a single ``Poll``. Django supports all the common database relationships:
 | |
| many-to-ones, many-to-manys and one-to-ones.
 | |
| 
 | |
| .. _`Python path`: http://docs.python.org/tutorial/modules.html#the-module-search-path
 | |
| 
 | |
| Activating models
 | |
| =================
 | |
| 
 | |
| That small bit of model code gives Django a lot of information. With it, Django
 | |
| is able to:
 | |
| 
 | |
| * Create a database schema (``CREATE TABLE`` statements) for this app.
 | |
| * Create a Python database-access API for accessing ``Poll`` and ``Choice`` objects.
 | |
| 
 | |
| But first we need to tell our project that the ``polls`` app is installed.
 | |
| 
 | |
| .. admonition:: Philosophy
 | |
| 
 | |
|     Django apps are "pluggable": You can use an app in multiple projects, and
 | |
|     you can distribute apps, because they don't have to be tied to a given
 | |
|     Django installation.
 | |
| 
 | |
| Edit the :file:`mysite/settings.py` file again, and change the
 | |
| :setting:`INSTALLED_APPS` setting to include the string ``'polls'``. So it'll
 | |
| look like this::
 | |
| 
 | |
|     INSTALLED_APPS = (
 | |
|         'django.contrib.admin',
 | |
|         'django.contrib.auth',
 | |
|         'django.contrib.contenttypes',
 | |
|         'django.contrib.sessions',
 | |
|         'django.contrib.messages',
 | |
|         'django.contrib.staticfiles',
 | |
|         'polls',
 | |
|     )
 | |
| 
 | |
| Now Django knows to include the ``polls`` app. Let's run another command:
 | |
| 
 | |
| .. code-block:: bash
 | |
| 
 | |
|     $ python manage.py sql polls
 | |
| 
 | |
| You should see something similar to the following (the ``CREATE TABLE`` SQL
 | |
| statements for the polls app):
 | |
| 
 | |
| .. code-block:: sql
 | |
| 
 | |
|     BEGIN;
 | |
|     CREATE TABLE "polls_poll" (
 | |
|         "id" integer NOT NULL PRIMARY KEY,
 | |
|         "question" varchar(200) NOT NULL,
 | |
|         "pub_date" datetime NOT NULL
 | |
|     );
 | |
|     CREATE TABLE "polls_choice" (
 | |
|         "id" integer NOT NULL PRIMARY KEY,
 | |
|         "poll_id" integer NOT NULL REFERENCES "polls_poll" ("id"),
 | |
|         "choice_text" varchar(200) NOT NULL,
 | |
|         "votes" integer NOT NULL
 | |
|     );
 | |
|     COMMIT;
 | |
| 
 | |
| Note the following:
 | |
| 
 | |
| * The exact output will vary depending on the database you are using. The
 | |
|   example above is generated for SQLite.
 | |
| 
 | |
| * Table names are automatically generated by combining the name of the app
 | |
|   (``polls``) and the lowercase name of the model -- ``poll`` and
 | |
|   ``choice``. (You can override this behavior.)
 | |
| 
 | |
| * Primary keys (IDs) are added automatically. (You can override this, too.)
 | |
| 
 | |
| * By convention, Django appends ``"_id"`` to the foreign key field name.
 | |
|   (Yes, you can override this, as well.)
 | |
| 
 | |
| * The foreign key relationship is made explicit by a ``REFERENCES``
 | |
|   statement.
 | |
| 
 | |
| * It's tailored to the database you're using, so database-specific field
 | |
|   types such as ``auto_increment`` (MySQL), ``serial`` (PostgreSQL), or
 | |
|   ``integer primary key`` (SQLite) are handled for you automatically. Same
 | |
|   goes for quoting of field names -- e.g., using double quotes or single
 | |
|   quotes.
 | |
| 
 | |
| * The :djadmin:`sql` command doesn't actually run the SQL in your database -
 | |
|   it just prints it to the screen so that you can see what SQL Django thinks
 | |
|   is required. If you wanted to, you could copy and paste this SQL into your
 | |
|   database prompt. However, as we will see shortly, Django provides an
 | |
|   easier way of committing the SQL to the database.
 | |
| 
 | |
| If you're interested, also run the following commands:
 | |
| 
 | |
| * :djadmin:`python manage.py validate <validate>` -- Checks for any errors
 | |
|   in the construction of your models.
 | |
| 
 | |
| * :djadmin:`python manage.py sqlcustom polls <sqlcustom>` -- Outputs any
 | |
|   :ref:`custom SQL statements <initial-sql>` (such as table modifications or
 | |
|   constraints) that are defined for the application.
 | |
| 
 | |
| * :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 parameters were {'id': 2}
 | |
| 
 | |
|     # 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.
 |