tutorial02.txt

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

By Adrian Holovaty <holovaty@gmail.com>

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

.. _Tutorial 1: http://www.djangoproject.com/documentation/tutorial1/

.. 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 ``INSTALLED_APPS`` setting.
    * Run the command ``django-admin.py install admin``. This will create an
      extra database table that the admin needs.
    * Edit your ``myproject.urls`` file and uncomment the line below
      "Uncomment this for admin:". 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.

Create a user account
=====================

Run the following command to create a superuser account for your admin site::

    django-admin.py createsuperuser --settings=myproject.settings

The script will prompt you for a username, e-mail address and password (twice).

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

To make things easy, Django comes with a pure-Python Web server that builds on
the BaseHTTPServer included in Python's standard library. Let's start the
server and explore the admin site.

Just run the following command to start the server::

    django-admin.py runserver --settings=myproject.settings

It'll start a Web server running locally -- on port 8000, by default. If you
want to change the server's port, pass it as a command-line argument::

    django-admin.py runserver 8080 --settings=myproject.settings

DON'T use this server in anything resembling a production environment. It's
intended only for use while developing.

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:: http://media.djangoproject.com/img/doc/tutorial/admin01.png
   :alt: Django admin login screen

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

Now, try logging in. You should see the Django admin index page:

.. image:: http://media.djangoproject.com/img/doc/tutorial/admin02t.png
   :alt: Django admin index page
   :target: http://media.djangoproject.com/img/doc/tutorial/admin02.png

By default, you should see two types of editable content: groups and users.
These are core features Django ships with by default.

.. _"I can't log in" questions: http://www.djangoproject.com/documentation/faq/#the-admin-site

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 specify in the ``polls.Poll`` model that Poll
objects have an admin interface. Edit the ``myproject/apps/polls/models/polls.py``
file and make the following change to add an inner ``META`` class with an
``admin`` attribute::

    class Poll(meta.Model):
        # ...
        class META:
            admin = meta.Admin()

The ``class META`` contains all non-field metadata about this model.

Now reload the Django admin page to see your changes. Note that you don't have
to restart the development server -- it auto-reloads code.

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

Now that ``Poll`` has the ``admin`` attribute, Django knows that it should be
displayed on the admin index page:

.. image:: http://media.djangoproject.com/img/doc/tutorial/admin03t.png
   :alt: Django admin index page, now with polls displayed
   :target: http://media.djangoproject.com/img/doc/tutorial/admin03.png

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:: http://media.djangoproject.com/img/doc/tutorial/admin04t.png
   :alt: Polls change list page
   :target: http://media.djangoproject.com/img/doc/tutorial/admin04.png

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

.. image:: http://media.djangoproject.com/img/doc/tutorial/admin05t.png
   :alt: Editing form for poll object
   :target: http://media.djangoproject.com/img/doc/tutorial/admin05.png

Things to note here:

* The form is automatically generated from the Poll model.
* The different model field types (``meta.DateTimeField``, ``meta.CharField``)
  correspond to the appropriate HTML input widget. Each type of field knows
  how to display itself in the Django admin.
* Each ``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:: http://media.djangoproject.com/img/doc/tutorial/admin06t.png
   :alt: History page for poll object
   :target: http://media.djangoproject.com/img/doc/tutorial/admin06.png

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

Take a few minutes to marvel at all the code you didn't have to write.

Let's customize this a bit. We can reorder the fields by explicitly adding a
``fields`` parameter to ``meta.Admin``::

        admin = meta.Admin(
            fields = (
                (None, {'fields': ('pub_date', 'question')}),
            ),
        )

That made the "Publication date" show up first instead of second:

.. image:: http://media.djangoproject.com/img/doc/tutorial/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::

        admin = meta.Admin(
            fields = (
                (None, {'fields': ('question',)}),
                ('Date information', {'fields': ('pub_date',)}),
            ),
        )

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

.. image:: http://media.djangoproject.com/img/doc/tutorial/admin08t.png
   :alt: Form has fieldsets now
   :target: http://media.djangoproject.com/img/doc/tutorial/admin08.png

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::

        admin = meta.Admin(
            fields = (
                (None, {'fields': ('question',)}),
                ('Date information', {'fields': ('pub_date',), 'classes': 'collapse'}),
            ),
        )

.. image:: http://media.djangoproject.com/img/doc/tutorial/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.

In this case, there are two ways to solve this problem. The first is to give
the ``Choice`` model its own ``admin`` attribute, just as we did with ``Poll``.
Here's what that would look like::

    class Choice(meta.Model):
        # ...
        class META:
            admin = meta.Admin()

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

.. image:: http://media.djangoproject.com/img/doc/tutorial/admin10.png
   :alt: Choice admin page

In that form, the "Poll" field is a select box containing every poll in the
database. 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 ``admin`` for the Choice model. Then, edit the ``ForeignKey(Poll)``
field like so::

    poll = meta.ForeignKey(Poll, edit_inline=meta.STACKED, num_in_admin=3)

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

Then change the other fields in ``Choice`` to give them ``core=True``::

    choice = meta.CharField(maxlength=200, core=True)
    votes = meta.IntegerField(core=True)

This tells Django: "When you edit a Choice on the Poll admin page, the 'choice'
and 'votes' fields are required. The presence of at least one of them signifies
the addition of a new Choice object, and clearing both of them signifies the
deletion of that existing Choice object."

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

.. image:: http://media.djangoproject.com/img/doc/tutorial/admin11t.png
   :alt: Add poll page now has choices on it
   :target: http://media.djangoproject.com/img/doc/tutorial/admin11.png

It works like this: There are three slots for related Choices -- as specified
by ``num_in_admin`` -- but each time you come back to the "Change" page for an
already-created object, you get one extra slot. (This means there's no
hard-coded limit on how many related objects can be added.) If you wanted space
for three extra Choices each time you changed the poll, you'd use
``num_extra_on_change=3``.

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 an
alternate way of displaying inline related objects::

    poll = meta.ForeignKey(Poll, edit_inline=meta.TABULAR, num_in_admin=3)

With that ``edit_inline=meta.TABULAR`` (instead of ``meta.STACKED``), the
related objects are displayed in a more compact, table-based format:

.. image:: http://media.djangoproject.com/img/doc/tutorial/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:: http://media.djangoproject.com/img/doc/tutorial/admin04t.png
   :alt: Polls change list page
   :target: http://media.djangoproject.com/img/doc/tutorial/admin04.png

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

    class Poll(meta.Model):
        # ...
        class META:
            admin = meta.Admin(
                # ...
                list_display = ('question', 'pub_date'),
            )

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

    list_display = ('question', 'pub_date', 'was_published_today'),

Now the poll change list page looks like this:

.. image:: http://media.djangoproject.com/img/doc/tutorial/admin13t.png
   :alt: Polls change list page, updated
   :target: http://media.djangoproject.com/img/doc/tutorial/admin13.png

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 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 ``Poll.admin``::

    list_filter = ['pub_date'],

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

.. image:: http://media.djangoproject.com/img/doc/tutorial/admin14t.png
   :alt: Polls change list page, updated
   :target: http://media.djangoproject.com/img/doc/tutorial/admin14.png

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" and "example.com" 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 (``myproject/settings.py``, remember) and look at the
``TEMPLATE_DIRS`` setting. ``TEMPLATE_DIRS`` is a tuple of filesystem
directories to check when loading Django templates. It's a search path.

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

    TEMPLATE_DIRS = (
        "/home/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 ``TEMPLATE_DIRS``. For
example, if your ``TEMPLATE_DIRS`` includes ``"/home/mytemplates"``, as above,
then copy ``django/contrib/admin/templates/admin/base_site.html`` to
``/home/mytemplates/admin/base_site.html``.

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

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 ``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 `loader types documentation`_ for full
information.

.. _loader types documentation: http://www.djangoproject.com/documentation/templates_python/#loader-types

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 available apps, according to your ``INSTALLED_APPS``
setting. But the order in which it displays things is random, and 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 tag called ``{% get_admin_app_list as app_list %}``. That's the
magic that retrieves 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.

Django offers another shortcut in this department. Run the command
``django-admin.py adminindex polls`` to get a chunk of template code for
inclusion in the admin index template. It's a useful starting point.

For full details on customizing the look and feel of the Django admin site in
general, see the `Django admin CSS guide`_.

When you're comfortable with the admin site, read `part 3 of this tutorial`_ to
start working on public poll views.

.. _Django admin CSS guide: http://www.djangoproject.com/documentation/admin_css/
.. _part 3 of this tutorial: http://www.djangoproject.com/documentation/tutorial3/