tutorial02.txt

.. _intro-tutorial02:

=====================================
Writing your first Django app, part 2
=====================================

This tutorial begins where :ref:`Tutorial 1 <intro-tutorial01>` left off. We're
continuing the Web-poll application and will focus on Django's
automatically-generated admin site.

.. admonition:: Philosophy

    Generating admin sites for your staff or clients to add, change and delete
    content is tedious work that doesn't require much creativity. For that
    reason, Django entirely automates creation of admin interfaces for models.

    Django was written in a newsroom environment, with a very clear separation
    between "content publishers" and the "public" site. Site managers use the
    system to add news stories, events, sports scores, etc., and that content is
    displayed on the public site. Django solves the problem of creating a
    unified interface for site administrators to edit content.

    The admin isn't necessarily intended to be used by site visitors; it's for
    site managers.

Activate the admin site
=======================

The Django admin site is not activated by default -- it's an opt-in thing. To
activate the admin site for your installation, do these three things:

    * Add ``"django.contrib.admin"`` to your :setting:`INSTALLED_APPS` setting.

    * Run ``python manage.py syncdb``. Since you have added a new application
      to :setting:`INSTALLED_APPS`, the database tables need to be updated.

    * Edit your ``mysite/urls.py`` file and uncomment the lines that reference
      the admin -- there are three lines in total to uncomment. This file is a
      URLconf; we'll dig into URLconfs in the next tutorial. For now, all you
      need to know is that it maps URL roots to applications. In the end, you
      should have a ``urls.py`` file that looks like this:

    .. versionchanged:: 1.1
        The method for adding admin urls has changed in Django 1.1.

      .. parsed-literal::

          from django.conf.urls.defaults import *

          # Uncomment the next two lines to enable the admin:
          **from django.contrib import admin**
          **admin.autodiscover()**

          urlpatterns = patterns('',
              # Example:
              # (r'^mysite/', include('mysite.foo.urls')),

              # Uncomment the admin/doc line below and add 'django.contrib.admindocs'
              # to INSTALLED_APPS to enable admin documentation:
              # (r'^admin/doc/', include('django.contrib.admindocs.urls')),

              # Uncomment the next line to enable the admin:
              **(r'^admin/', include(admin.site.urls)),**
          )

      (The bold lines are the ones that needed to be uncommented.)

Start the development server
============================

Let's start the development server and explore the admin site.

Recall from Tutorial 1 that you start the development server like so:

.. code-block:: bash

    python manage.py runserver

Now, open a Web browser and go to "/admin/" on your local domain -- e.g.,
http://127.0.0.1:8000/admin/. You should see the admin's login screen:

.. image:: _images/admin01.png
   :alt: Django admin login screen

Enter the admin site
====================

Now, try logging in. (You created a superuser account in the first part of this
tutorial, remember?  If you didn't create one or forgot the password you can
:ref:`create another one <topics-auth-creating-superusers>`.) You should see
the Django admin index page:

.. image:: _images/admin02t.png
   :alt: Django admin index page

You should see a few other types of editable content, including groups, users
and sites. These are core features Django ships with by default.

Make the poll app modifiable in the admin
=========================================

But where's our poll app? It's not displayed on the admin index page.

Just one thing to do: We need to tell the admin that ``Poll``
objects have an admin interface. To do this, create a file called
``admin.py`` in your ``polls`` directory, and edit it to look like this::

    from mysite.polls.models import Poll
    from django.contrib import admin

    admin.site.register(Poll)

You'll need to restart the development server to see your changes. Normally,
the server auto-reloads code every time you modify a file, but the action of
creating a new file doesn't trigger the auto-reloading logic.

Explore the free admin functionality
====================================

Now that we've registered ``Poll``, Django knows that it should be displayed on
the admin index page:

.. image:: _images/admin03t.png
   :alt: Django admin index page, now with polls displayed

Click "Polls." Now you're at the "change list" page for polls. This page
displays all the polls in the database and lets you choose one to change it.
There's the "What's up?" poll we created in the first tutorial:

.. image:: _images/admin04t.png
   :alt: Polls change list page

Click the "What's up?" poll to edit it:

.. image:: _images/admin05t.png
   :alt: Editing form for poll object

Things to note here:

    * The form is automatically generated from the Poll model.

    * The different model field types (:class:`~django.db.models.DateTimeField`,
      :class:`~django.db.models.CharField`) correspond to the appropriate HTML
      input widget. Each type of field knows how to display itself in the Django
      admin.

    * Each :class:`~django.db.models.DateTimeField` gets free JavaScript
      shortcuts. Dates get a "Today" shortcut and calendar popup, and times get
      a "Now" shortcut and a convenient popup that lists commonly entered times.

The bottom part of the page gives you a couple of options:

    * Save -- Saves changes and returns to the change-list page for this type of
      object.

    * Save and continue editing -- Saves changes and reloads the admin page for
      this object.

    * Save and add another -- Saves changes and loads a new, blank form for this
      type of object.

    * Delete -- Displays a delete confirmation page.

Change the "Date published" by clicking the "Today" and "Now" shortcuts. Then
click "Save and continue editing." Then click "History" in the upper right.
You'll see a page listing all changes made to this object via the Django admin,
with the timestamp and username of the person who made the change:

.. image:: _images/admin06t.png
   :alt: History page for poll object

Customize the admin form
========================

Take a few minutes to marvel at all the code you didn't have to write. By
registering the Poll model with ``admin.site.register(Poll)``, Django was able
to construct a default form representation. Often, you'll want to customize how
the admin form looks and works. You'll do this by telling Django the options
you want when you register the object.

Let's see how this works by re-ordering the fields on the edit form. Replace
the ``admin.site.register(Poll)`` line with::

    class PollAdmin(admin.ModelAdmin):
        fields = ['pub_date', 'question']

    admin.site.register(Poll, PollAdmin)

You'll follow this pattern -- create a model admin object, then pass it as the
second argument to ``admin.site.register()`` -- any time you need to change the
admin options for an object.

This particular change above makes the "Publication date" come before the
"Question" field:

.. image:: _images/admin07.png
   :alt: Fields have been reordered

This isn't impressive with only two fields, but for admin forms with dozens
of fields, choosing an intuitive order is an important usability detail.

And speaking of forms with dozens of fields, you might want to split the form
up into fieldsets::

    class PollAdmin(admin.ModelAdmin):
        fieldsets = [
            (None,               {'fields': ['question']}),
            ('Date information', {'fields': ['pub_date']}),
        ]

    admin.site.register(Poll, PollAdmin)

The first element of each tuple in ``fieldsets`` is the title of the fieldset.
Here's what our form looks like now:

.. image:: _images/admin08t.png
   :alt: Form has fieldsets now

You can assign arbitrary HTML classes to each fieldset. Django provides a
``"collapse"`` class that displays a particular fieldset initially collapsed.
This is useful when you have a long form that contains a number of fields that
aren't commonly used::

        class PollAdmin(admin.ModelAdmin):
            fieldsets = [
                (None,               {'fields': ['question']}),
                ('Date information', {'fields': ['pub_date'], 'classes': ['collapse']}),
            ]

.. image:: _images/admin09.png
   :alt: Fieldset is initially collapsed

Adding related objects
======================

OK, we have our Poll admin page. But a ``Poll`` has multiple ``Choices``, and
the admin page doesn't display choices.

Yet.

There are two ways to solve this problem. The first is to register ``Choice``
with the admin just as we did with ``Poll``. That's easy::

    from mysite.polls.models import Choice

    admin.site.register(Choice)

Now "Choices" is an available option in the Django admin. The "Add choice" form
looks like this:

.. image:: _images/admin10.png
   :alt: Choice admin page

In that form, the "Poll" field is a select box containing every poll in the
database. Django knows that a :class:`~django.db.models.ForeignKey` should be
represented in the admin as a ``<select>`` box. In our case, only one poll
exists at this point.

Also note the "Add Another" link next to "Poll." Every object with a
``ForeignKey`` relationship to another gets this for free. When you click "Add
Another," you'll get a popup window with the "Add poll" form. If you add a poll
in that window and click "Save," Django will save the poll to the database and
dynamically add it as the selected choice on the "Add choice" form you're
looking at.

But, really, this is an inefficient way of adding Choice objects to the system.
It'd be better if you could add a bunch of Choices directly when you create the
Poll object. Let's make that happen.

Remove the ``register()`` call for the Choice model. Then, edit the ``Poll``
registration code to read::

    class ChoiceInline(admin.StackedInline):
        model = Choice
        extra = 3

    class PollAdmin(admin.ModelAdmin):
        fieldsets = [
            (None,               {'fields': ['question']}),
            ('Date information', {'fields': ['pub_date'], 'classes': ['collapse']}),
        ]
        inlines = [ChoiceInline]

    admin.site.register(Poll, PollAdmin)

This tells Django: "Choice objects are edited on the Poll admin page. By
default, provide enough fields for 3 choices."

Load the "Add poll" page to see how that looks:

.. image:: _images/admin11t.png
   :alt: Add poll page now has choices on it

It works like this: There are three slots for related Choices -- as specified
by ``extra`` -- and each time you come back to the "Change" page for an
already-created object, you get another three extra slots.

One small problem, though. It takes a lot of screen space to display all the
fields for entering related Choice objects. For that reason, Django offers a
tabular way of displaying inline related objects; you just need to change
the ``ChoiceInline`` declaration to read::

    class ChoiceInline(admin.TabularInline):
        #...

With that ``TabularInline`` (instead of ``StackedInline``), the
related objects are displayed in a more compact, table-based format:

.. image:: _images/admin12.png
   :alt: Add poll page now has more compact choices

Customize the admin change list
===============================

Now that the Poll admin page is looking good, let's make some tweaks to the
"change list" page -- the one that displays all the polls in the system.

Here's what it looks like at this point:

.. image:: _images/admin04t.png
   :alt: Polls change list page

By default, Django displays the ``str()`` of each object. But sometimes it'd be
more helpful if we could display individual fields. To do that, use the
``list_display`` admin option, which is a tuple of field names to display, as
columns, on the change list page for the object::

    class PollAdmin(admin.ModelAdmin):
        # ...
        list_display = ('question', 'pub_date')

Just for good measure, let's also include the ``was_published_today`` custom
method from Tutorial 1::

    class PollAdmin(admin.ModelAdmin):
        # ...
        list_display = ('question', 'pub_date', 'was_published_today')

Now the poll change list page looks like this:

.. image:: _images/admin13t.png
   :alt: Polls change list page, updated

You can click on the column headers to sort by those values -- except in the
case of the ``was_published_today`` header, because sorting by the output of
an arbitrary method is not supported. Also note that the column header for
``was_published_today`` is, by default, the name of the method (with
underscores replaced with spaces). But you can change that by giving that
method (in ``models.py``) a ``short_description`` attribute::

    def was_published_today(self):
        return self.pub_date.date() == datetime.date.today()
    was_published_today.short_description = 'Published today?'

Let's add another improvement to the Poll change list page: Filters. Add the
following line to ``PollAdmin``::

    list_filter = ['pub_date']

That adds a "Filter" sidebar that lets people filter the change list by the
``pub_date`` field:

.. image:: _images/admin14t.png
   :alt: Polls change list page, updated

The type of filter displayed depends on the type of field you're filtering on.
Because ``pub_date`` is a DateTimeField, Django knows to give the default
filter options for DateTimeFields: "Any date," "Today," "Past 7 days,"
"This month," "This year."

This is shaping up well. Let's add some search capability::

    search_fields = ['question']

That adds a search box at the top of the change list. When somebody enters
search terms, Django will search the ``question`` field. You can use as many
fields as you'd like -- although because it uses a ``LIKE`` query behind the
scenes, keep it reasonable, to keep your database happy.

Finally, because Poll objects have dates, it'd be convenient to be able to
drill down by date. Add this line::

    date_hierarchy = 'pub_date'

That adds hierarchical navigation, by date, to the top of the change list page.
At top level, it displays all available years. Then it drills down to months
and, ultimately, days.

Now's also a good time to note that change lists give you free pagination. The
default is to display 50 items per page. Change-list pagination, search boxes,
filters, date-hierarchies and column-header-ordering all work together like you
think they should.

Customize the admin look and feel
=================================

Clearly, having "Django administration" at the top of each admin page is
ridiculous. It's just placeholder text.

That's easy to change, though, using Django's template system. The Django admin
is powered by Django itself, and its interfaces use Django's own template
system. (How meta!)

Open your settings file (``mysite/settings.py``, remember) and look at the
:setting:`TEMPLATE_DIRS` setting. :setting:`TEMPLATE_DIRS` is a tuple of
filesystem directories to check when loading Django templates. It's a search
path.

By default, :setting:`TEMPLATE_DIRS` is empty. So, let's add a line to it, to
tell Django where our templates live::

    TEMPLATE_DIRS = (
        "/home/my_username/mytemplates", # Change this to your own directory.
    )

Now copy the template ``admin/base_site.html`` from within the default Django
admin template directory (``django/contrib/admin/templates``) into an ``admin``
subdirectory of whichever directory you're using in :setting:`TEMPLATE_DIRS`.
For example, if your :setting:`TEMPLATE_DIRS` includes
``"/home/my_username/mytemplates"``, as above, then copy
``django/contrib/admin/templates/admin/base_site.html`` to
``/home/my_username/mytemplates/admin/base_site.html``. Don't forget that
``admin`` subdirectory.

Then, just edit the file and replace the generic Django text with your own
site's name as you see fit.

This template file contains lots of text like ``{% block branding %}``
and ``{{ title }}. The ``{%`` and ``{{`` tags are part of Django's
template language. When Django renders ``admin/base_site.html``, this
template language will be evaluated to produce the final HTML page.
Don't worry if you can't make any sense of the template right now --
we'll delve into Django's templating language in Tutorial 3.

Note that any of Django's default admin templates can be overridden. To
override a template, just do the same thing you did with ``base_site.html`` --
copy it from the default directory into your custom directory, and make
changes.

Astute readers will ask: But if :setting:`TEMPLATE_DIRS` was empty by default,
how was Django finding the default admin templates? The answer is that, by
default, Django automatically looks for a ``templates/`` subdirectory within
each app package, for use as a fallback. See the :ref:`template loader
documentation <template-loaders>` for full information.

Customize the admin index page
==============================

On a similar note, you might want to customize the look and feel of the Django
admin index page.

By default, it displays all the apps in :setting:`INSTALLED_APPS` that have been
registered with the admin application, in alphabetical order. You may want to
make significant changes to the layout. After all, the index is probably the
most important page of the admin, and it should be easy to use.

The template to customize is ``admin/index.html``. (Do the same as with
``admin/base_site.html`` in the previous section -- copy it from the default
directory to your custom template directory.) Edit the file, and you'll see it
uses a template variable called ``app_list``. That variable contains every
installed Django app. Instead of using that, you can hard-code links to
object-specific admin pages in whatever way you think is best. Again,
don't worry if you can't understand the template language -- we'll cover that
in more detail in Tutorial 3.

When you're comfortable with the admin site, read :ref:`part 3 of this tutorial
<intro-tutorial03>` to start working on public poll views.