author | Lennard de Rijk <ljvderijk@gmail.com> |
Mon, 13 Jul 2009 00:53:42 +0200 | |
changeset 2616 | 9321e100a7fb |
parent 109 | 620f9b141567 |
permissions | -rw-r--r-- |
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===================================== |
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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 poll. |
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We'll assume you have `Django installed`_ already. You can tell Django is |
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installed by running the Python interactive interpreter and typing |
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``import django``. If that command runs successfully, with no errors, Django is |
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installed. |
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.. _`Django installed`: ../install/ |
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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`` and we'll |
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try to help. |
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.. _django-users: http://groups.google.com/group/django-users |
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.. _#django: irc://irc.freenode.net/django |
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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 |
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a Django *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 command ``django-admin.py startproject mysite``. This |
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will create a ``mysite`` directory in your current directory. |
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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 ``site`` (which |
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conflicts with a built-in Python package). |
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(``django-admin.py`` should be on your system path if you installed Django via |
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``python setup.py``. If it's not on your path, you can find it in |
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``site-packages/django/bin``, where ``site-packages`` is a directory within |
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your Python installation. Consider symlinking to ``django-admin.py`` from some |
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place on your path, such as ``/usr/local/bin``.) |
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.. admonition:: Where should this code live? |
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If your background is in PHP, you're probably used to putting code under the |
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Web server's document root (in a place such as ``/var/www``). With Django, |
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you don't do that. It's not a good idea to put any of this Python code within |
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your Web server's document root, because it risks the possibility that |
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people may be able to view your code over the Web. That's not good for |
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security. |
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Put your code in some directory **outside** of the document root, such as |
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``/home/mycode``. |
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Let's look at what ``startproject`` created:: |
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mysite/ |
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__init__.py |
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manage.py |
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settings.py |
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urls.py |
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These files are: |
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* ``__init__.py``: An empty file that tells Python that this directory |
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should be considered a Python package. (Read `more about packages`_ in the |
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official Python docs if you're a Python beginner.) |
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* ``manage.py``: A command-line utility that lets you interact with this |
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Django project in various ways. |
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* ``settings.py``: Settings/configuration for this Django project. |
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* ``urls.py``: The URL declarations for this Django project; a "table of |
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contents" of your Django-powered site. |
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.. _more about packages: http://docs.python.org/tut/node8.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 ``mysite`` directory, if you |
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haven't already, and run the command ``python manage.py runserver``. You'll see |
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the following output on the command line:: |
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Validating models... |
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0 errors found. |
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Django version 0.95, using settings 'mysite.settings' |
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Development server is running at http://127.0.0.1:8000/ |
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Quit the server with CONTROL-C (Unix) or CTRL-BREAK (Windows). |
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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 ``runserver`` command starts the development server on port |
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8000. If you want to change the server's port, pass it as a command-line |
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argument. For instance, this command starts the server on port 8080:: |
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123 |
python manage.py runserver 8080 |
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Full docs for the development server are at `django-admin documentation`_. |
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126 |
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.. _django-admin documentation: ../django_admin/ |
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128 |
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129 |
Database setup |
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-------------- |
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131 |
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Now, edit ``settings.py``. It's a normal Python module with module-level |
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variables representing Django settings. Change these settings to match your |
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database's connection parameters: |
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135 |
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* ``DATABASE_ENGINE`` -- Either 'postgresql', 'mysql' or 'sqlite3'. |
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More coming soon. |
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* ``DATABASE_NAME`` -- The name of your database, or the full (absolute) |
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path to the database file if you're using SQLite. |
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* ``DATABASE_USER`` -- Your database username (not used for SQLite). |
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* ``DATABASE_PASSWORD`` -- Your database password (not used for SQLite). |
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* ``DATABASE_HOST`` -- The host your database is on. Leave this as an |
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empty string if your database server is on the same physical machine |
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(not used for SQLite). |
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145 |
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.. admonition:: Note |
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147 |
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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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151 |
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While you're editing ``settings.py``, take note of the ``INSTALLED_APPS`` |
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setting towards the bottom of the file. That variable holds the names of all |
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Django applications that are activated in this Django instance. Apps can be |
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used in multiple projects, and you can package and distribute them for use |
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by others in their projects. |
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157 |
|
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By default, ``INSTALLED_APPS`` contains the following apps, all of which come |
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with Django: |
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160 |
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* ``django.contrib.auth`` -- An authentication system. |
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* ``django.contrib.contenttypes`` -- A framework for content types. |
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* ``django.contrib.sessions`` -- A session framework. |
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* ``django.contrib.sites`` -- A framework for managing multiple sites |
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with one Django installation. |
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166 |
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These applications are included by default as a convenience for the common |
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case. |
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169 |
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Each 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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173 |
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174 |
python manage.py syncdb |
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175 |
|
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The ``syncdb`` command looks at the ``INSTALLED_APPS`` setting and creates any |
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necessary database tables according to the database settings in your |
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``settings.py`` file. You'll see a message for each database table it creates, |
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and you'll get a prompt asking you if you'd like to create a superuser account |
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for the authentication system. Go ahead and do that. |
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181 |
|
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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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184 |
display the tables Django created. |
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185 |
|
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186 |
.. admonition:: For the minimalists |
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187 |
|
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188 |
Like we said above, the default applications are included for the common |
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189 |
case, but not everybody needs them. If you don't need any or all of them, |
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190 |
feel free to comment-out or delete the appropriate line(s) from |
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191 |
``INSTALLED_APPS`` before running ``syncdb``. The ``syncdb`` command will |
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only create tables for apps in ``INSTALLED_APPS``. |
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193 |
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Creating models |
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195 |
=============== |
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196 |
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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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199 |
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Each application you write in Django consists of a Python package, somewhere |
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on your `Python path`_, that follows a certain convention. Django comes with a |
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utility that automatically generates the basic directory structure of an app, |
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so you can focus on writing code rather than creating directories. |
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.. admonition:: Projects vs. apps |
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206 |
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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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In this tutorial, we'll create our poll app in the ``mysite`` directory, |
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for simplicity. As a consequence, the app will be coupled to the project -- |
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that is, Python code within the poll app will refer to ``mysite.polls``. |
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Later in this tutorial, we'll discuss decoupling your apps for distribution. |
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217 |
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To create your app, make sure you're in the ``mysite`` directory and type |
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this command:: |
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python manage.py startapp polls |
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222 |
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That'll create a directory ``polls``, which is laid out like this:: |
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polls/ |
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__init__.py |
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models.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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234 |
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.. admonition:: Philosophy |
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236 |
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A model is the single, definitive source of data about your |
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data. It contains the essential fields and behaviors of the data you're |
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storing. Django follows the `DRY Principle`_. The goal is to define your |
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data model in one place and automatically derive things from it. |
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241 |
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In our simple poll app, we'll create two models: polls and choices. A poll has |
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a question and a publication date. A choice has two fields: the text of the |
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choice and a vote tally. Each choice is associated with a poll. |
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These concepts are represented by simple Python classes. Edit the |
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``polls/models.py`` file so it looks like this:: |
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from django.db import models |
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250 |
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class Poll(models.Model): |
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question = models.CharField(maxlength=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 = models.CharField(maxlength=200) |
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votes = models.IntegerField() |
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|
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The code is straightforward. Each model is represented by a class that |
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subclasses ``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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|
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Each field is represented by an instance of a ``models.*Field`` class -- e.g., |
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``models.CharField`` for character fields and ``models.DateTimeField`` for |
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datetimes. This tells Django what type of data each field holds. |
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267 |
|
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The name of each ``models.*Field`` instance (e.g. ``question`` or ``pub_date`` ) |
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is the field's name, in machine-friendly format. You'll use this value in your |
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Python code, and your database will use it as the column name. |
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|
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You can use an optional first positional argument to a ``Field`` to designate a |
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human-readable name. That's used in a couple of introspective parts of Django, |
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and it doubles as documentation. If this field isn't provided, Django will use |
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the machine-readable name. In this example, we've only defined a human-readable |
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name for ``Poll.pub_date``. For all other fields in this model, the field's |
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machine-readable name will suffice as its human-readable name. |
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|
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Some ``Field`` classes have required elements. ``CharField``, for example, |
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requires that you give it a ``maxlength``. That's used not only in the database |
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schema, but in validation, as we'll soon see. |
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|
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Finally, note a relationship is defined, using ``models.ForeignKey``. That tells |
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Django each Choice is related to a single Poll. Django supports all the common |
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database relationships: many-to-ones, many-to-manys and one-to-ones. |
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286 |
|
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.. _`Python path`: http://docs.python.org/tut/node8.html#SECTION008110000000000000000 |
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.. _DRY Principle: http://c2.com/cgi/wiki?DontRepeatYourself |
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289 |
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Activating models |
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================= |
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292 |
|
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That small bit of model code gives Django a lot of information. With it, Django |
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294 |
is able to: |
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295 |
|
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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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298 |
|
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But first we need to tell our project that the ``polls`` app is installed. |
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300 |
|
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.. admonition:: Philosophy |
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302 |
|
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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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306 |
|
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Edit the ``settings.py`` file again, and change the ``INSTALLED_APPS`` setting |
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to include the string ``'mysite.polls'``. So it'll look like this:: |
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309 |
|
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INSTALLED_APPS = ( |
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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.sites', |
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'mysite.polls' |
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) |
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|
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Now Django knows ``mysite`` includes the ``polls`` app. Let's run another command:: |
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319 |
|
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python manage.py sql polls |
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|
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You should see the following (the CREATE TABLE SQL statements for the polls app):: |
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323 |
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BEGIN; |
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CREATE TABLE "polls_poll" ( |
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"id" serial NOT NULL PRIMARY KEY, |
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"question" varchar(200) NOT NULL, |
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"pub_date" timestamp with time zone NOT NULL |
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); |
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CREATE TABLE "polls_choice" ( |
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"id" serial NOT NULL PRIMARY KEY, |
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"poll_id" integer NOT NULL REFERENCES "polls_poll" ("id"), |
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"choice" varchar(200) NOT NULL, |
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|
334 |
"votes" integer NOT NULL |
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335 |
); |
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336 |
COMMIT; |
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337 |
|
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338 |
Note the following: |
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339 |
|
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340 |
* Table names are automatically generated by combining the name of the app |
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341 |
(``polls``) and the lowercase name of the model -- ``poll`` and |
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342 |
``choice``. (You can override this behavior.) |
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343 |
|
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344 |
* Primary keys (IDs) are added automatically. (You can override this, too.) |
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345 |
|
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346 |
* By convention, Django appends ``"_id"`` to the foreign key field name. |
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347 |
Yes, you can override this, as well. |
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348 |
|
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349 |
* The foreign key relationship is made explicit by a ``REFERENCES`` statement. |
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350 |
|
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351 |
* It's tailored to the database you're using, so database-specific field |
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352 |
types such as ``auto_increment`` (MySQL), ``serial`` (PostgreSQL), or |
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353 |
``integer primary key`` (SQLite) are handled for you automatically. Same |
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354 |
goes for quoting of field names -- e.g., using double quotes or single |
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355 |
quotes. The author of this tutorial runs PostgreSQL, so the example |
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356 |
output is in PostgreSQL syntax. |
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357 |
|
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358 |
* The `sql` command doesn't actually run the SQL in your database - it just |
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359 |
prints it to the screen so that you can see what SQL Django thinks is required. |
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360 |
If you wanted to, you could copy and paste this SQL into your database prompt. |
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361 |
However, as we will see shortly, Django provides an easier way of committing |
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362 |
the SQL to the database. |
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363 |
|
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364 |
If you're interested, also run the following commands: |
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365 |
* ``python manage.py validate polls`` -- Checks for any errors in the |
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366 |
construction of your models. |
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367 |
|
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368 |
* ``python manage.py sqlinitialdata polls`` -- Outputs any initial data |
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369 |
required for Django's admin framework and your models. |
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|
370 |
|
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371 |
* ``python manage.py sqlclear polls`` -- Outputs the necessary ``DROP |
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372 |
TABLE`` statements for this app, according to which tables already exist |
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373 |
in your database (if any). |
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374 |
|
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|
375 |
* ``python manage.py sqlindexes polls`` -- Outputs the ``CREATE INDEX`` |
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376 |
statements for this app. |
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|
377 |
|
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|
378 |
* ``python manage.py sqlall polls`` -- A combination of all the SQL from |
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|
379 |
the 'sql', 'sqlinitialdata', and 'sqlindexes' commands. |
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|
380 |
|
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|
381 |
Looking at the output of those commands can help you understand what's actually |
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382 |
happening under the hood. |
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|
383 |
|
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|
384 |
Now, run ``syncdb`` again to create those model tables in your database:: |
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|
385 |
|
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|
386 |
python manage.py syncdb |
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|
387 |
|
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|
388 |
The ``syncdb`` command runs the sql from 'sqlall' on your database for all apps |
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|
389 |
in ``INSTALLED_APPS`` that don't already exist in your database. This creates |
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|
390 |
all the tables, initial data and indexes for any apps you have added to your |
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|
391 |
project since the last time you ran syncdb. ``syncdb`` can be called as often |
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|
392 |
as you like, and it will only ever create the tables that don't exist. |
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|
393 |
|
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|
394 |
Read the `django-admin.py documentation`_ for full information on what the |
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|
395 |
``manage.py`` utility can do. |
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|
396 |
|
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|
397 |
.. _django-admin.py documentation: ../django_admin/ |
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|
398 |
|
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|
399 |
Playing with the API |
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|
400 |
==================== |
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|
401 |
|
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|
402 |
Now, let's hop into the interactive Python shell and play around with the free |
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|
403 |
API Django gives you. To invoke the Python shell, use this command:: |
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|
404 |
|
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|
405 |
python manage.py shell |
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|
406 |
|
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|
407 |
We're using this instead of simply typing "python", because ``manage.py`` sets |
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parents:
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|
408 |
up the project's environment for you. "Setting up the environment" involves two |
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parents:
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|
409 |
things: |
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|
410 |
|
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parents:
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|
411 |
* Putting ``mysite`` on ``sys.path``. For flexibility, several pieces of |
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parents:
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|
412 |
Django refer to projects in Python dotted-path notation (e.g. |
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parents:
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|
413 |
``'mysite.polls.models'``). In order for this to work, the |
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|
414 |
``mysite`` package has to be on ``sys.path``. |
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|
415 |
|
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parents:
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|
416 |
We've already seen one example of this: the ``INSTALLED_APPS`` setting is |
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parents:
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|
417 |
a list of packages in dotted-path notation. |
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|
418 |
|
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parents:
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|
419 |
* Setting the ``DJANGO_SETTINGS_MODULE`` environment variable, which gives |
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parents:
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|
420 |
Django the path to your ``settings.py`` file. |
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|
421 |
|
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|
422 |
.. admonition:: Bypassing manage.py |
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|
423 |
|
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parents:
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|
424 |
If you'd rather not use ``manage.py``, no problem. Just make sure |
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parents:
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|
425 |
``mysite`` is at the root level on the Python path (i.e., |
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parents:
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|
426 |
``import mysite`` works) and set the ``DJANGO_SETTINGS_MODULE`` |
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parents:
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|
427 |
environment variable to ``mysite.settings``. |
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parents:
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|
428 |
|
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|
429 |
For more information on all of this, see the `django-admin.py documentation`_. |
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|
430 |
|
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|
431 |
Once you're in the shell, explore the database API:: |
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parents:
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|
432 |
|
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|
433 |
# Import the model classes we just wrote. |
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parents:
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|
434 |
>>> from mysite.polls.models import Poll, Choice |
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parents:
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|
435 |
|
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parents:
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|
436 |
# No polls are in the system yet. |
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|
437 |
>>> Poll.objects.all() |
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|
438 |
[] |
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|
439 |
|
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parents:
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|
440 |
# Create a new Poll. |
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parents:
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|
441 |
>>> from datetime import datetime |
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parents:
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|
442 |
>>> p = Poll(question="What's up?", pub_date=datetime.now()) |
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|
443 |
|
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|
444 |
# Save the object into the database. You have to call save() explicitly. |
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|
445 |
>>> p.save() |
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Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
446 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
447 |
# Now it has an ID. Note that this might say "1L" instead of "1", depending |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
448 |
# on which database you're using. That's no biggie; it just means your |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
449 |
# database backend prefers to return integers as Python long integer |
620f9b141567
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Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
450 |
# objects. |
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Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
451 |
>>> p.id |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
452 |
1 |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
453 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
454 |
# Access database columns via Python attributes. |
620f9b141567
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Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
455 |
>>> p.question |
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Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
456 |
"What's up?" |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
457 |
>>> p.pub_date |
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Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
458 |
datetime.datetime(2005, 7, 15, 12, 00, 53) |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
459 |
|
620f9b141567
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Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
460 |
# Change values by changing the attributes, then calling save(). |
620f9b141567
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Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
461 |
>>> p.pub_date = datetime(2005, 4, 1, 0, 0) |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
462 |
>>> p.save() |
620f9b141567
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Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
463 |
|
620f9b141567
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Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
464 |
# objects.all() displays all the polls in the database. |
620f9b141567
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Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
465 |
>>> Poll.objects.all() |
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Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
466 |
[<Poll: Poll object>] |
620f9b141567
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Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
467 |
|
620f9b141567
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Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
468 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
469 |
Wait a minute. ``<Poll: Poll object>`` is, utterly, an unhelpful |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
470 |
representation of this object. Let's fix that by editing the polls model (in |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
471 |
the ``polls/models.py`` file) and adding a ``__str__()`` method to both |
620f9b141567
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Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
472 |
``Poll`` and ``Choice``:: |
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Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
473 |
|
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Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
474 |
class Poll(models.Model): |
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Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
475 |
# ... |
620f9b141567
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Todd Larsen <tlarsen@google.com>
parents:
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changeset
|
476 |
def __str__(self): |
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Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
477 |
return self.question |
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Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
478 |
|
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Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
479 |
class Choice(models.Model): |
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Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
480 |
# ... |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
481 |
def __str__(self): |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
482 |
return self.choice |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
483 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
484 |
It's important to add ``__str__()`` methods to your models, not only for your |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
485 |
own sanity when dealing with the interactive prompt, but also because objects' |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
486 |
representations are used throughout Django's automatically-generated admin. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
487 |
|
620f9b141567
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Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
488 |
Note these are normal Python methods. Let's add a custom method, just for |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
489 |
demonstration:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
490 |
|
620f9b141567
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Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
491 |
import datetime |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
492 |
# ... |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
493 |
class Poll(models.Model): |
620f9b141567
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Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
494 |
# ... |
620f9b141567
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Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
495 |
def was_published_today(self): |
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Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
496 |
return self.pub_date.date() == datetime.date.today() |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
497 |
|
620f9b141567
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Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
498 |
Note the addition of ``import datetime`` to reference Python's standard |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
499 |
``datetime`` module. |
620f9b141567
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Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
500 |
|
620f9b141567
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Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
501 |
Let's jump back into the Python interactive shell by running |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
502 |
``python manage.py shell`` again:: |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
503 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
504 |
>>> from mysite.polls.models import Poll, Choice |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
505 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
506 |
# Make sure our __str__() addition worked. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
507 |
>>> Poll.objects.all() |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
508 |
[<Poll: What's up?>] |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
509 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
510 |
# Django provides a rich database lookup API that's entirely driven by |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
511 |
# keyword arguments. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
512 |
>>> Poll.objects.filter(id=1) |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
513 |
[<Poll: What's up?>] |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
514 |
>>> Poll.objects.filter(question__startswith='What') |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
515 |
[<Poll: What's up?>] |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
516 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
517 |
# Get the poll whose year is 2005. Of course, if you're going through this |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
518 |
# tutorial in another year, change as appropriate. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
519 |
>>> Poll.objects.get(pub_date__year=2005) |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
520 |
<Poll: What's up?> |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
521 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
522 |
>>> Poll.objects.get(id=2) |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
523 |
Traceback (most recent call last): |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
524 |
... |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
525 |
DoesNotExist: Poll matching query does not exist. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
526 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
527 |
# Lookup by a primary key is the most common case, so Django provides a |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
528 |
# shortcut for primary-key exact lookups. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
529 |
# The following is identical to Poll.objects.get(id=1). |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
530 |
>>> Poll.objects.get(pk=1) |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
531 |
<Poll: What's up?> |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
532 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
533 |
# Make sure our custom method worked. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
534 |
>>> p = Poll.objects.get(pk=1) |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
535 |
>>> p.was_published_today() |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
536 |
False |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
537 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
538 |
# Give the Poll a couple of Choices. The create call constructs a new |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
539 |
# choice object, does the INSERT statement, adds the choice to the set |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
540 |
# of available choices and returns the new Choice object. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
541 |
>>> p = Poll.objects.get(pk=1) |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
542 |
>>> p.choice_set.create(choice='Not much', votes=0) |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
543 |
<Choice: Not much> |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
544 |
>>> p.choice_set.create(choice='The sky', votes=0) |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
545 |
<Choice: The sky> |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
546 |
>>> c = p.choice_set.create(choice='Just hacking again', votes=0) |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
547 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
548 |
# Choice objects have API access to their related Poll objects. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
549 |
>>> c.poll |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
550 |
<Poll: What's up?> |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
551 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
552 |
# And vice versa: Poll objects get access to Choice objects. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
553 |
>>> p.choice_set.all() |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
554 |
[<Choice: Not much>, <Choice: The sky>, <Choice: Just hacking again>] |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
555 |
>>> p.choice_set.count() |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
556 |
3 |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
557 |
|
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
parents:
diff
changeset
|
558 |
# The API automatically follows relationships as far as you need. |
620f9b141567
Load ../../google_appengine into trunk/thirdparty/google_appengine.
Todd Larsen <tlarsen@google.com>
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559 |
# Use double underscores to separate relationships. |
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parents:
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# This works as many levels deep as you want. There's no limit. |
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parents:
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changeset
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561 |
# Find all Choices for any poll whose pub_date is in 2005. |
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parents:
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>>> Choice.objects.filter(poll__pub_date__year=2005) |
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parents:
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563 |
[<Choice: Not much>, <Choice: The sky>, <Choice: Just hacking again>] |
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564 |
|
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parents:
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565 |
# Let's delete one of the choices. Use delete() for that. |
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parents:
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>>> c = p.choice_set.filter(choice__startswith='Just hacking') |
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parents:
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567 |
>>> c.delete() |
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Todd Larsen <tlarsen@google.com>
parents:
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|
568 |
|
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569 |
For full details on the database API, see our `Database API reference`_. |
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parents:
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570 |
|
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|
571 |
When you're comfortable with the API, read `part 2 of this tutorial`_ to get |
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parents:
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572 |
Django's automatic admin working. |
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parents:
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|
573 |
|
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parents:
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574 |
.. _Database API reference: ../db_api/ |
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parents:
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.. _part 2 of this tutorial: ../tutorial2/ |