lib/django-1.2/docs/ref/contrib/admin/actions.txt

=============
Admin actions
=============

.. versionadded:: 1.1

.. currentmodule:: django.contrib.admin

The basic workflow of Django's admin is, in a nutshell, "select an object,
then change it." This works well for a majority of use cases. However, if you
need to make the same change to many objects at once, this workflow can be
quite tedious.

In these cases, Django's admin lets you write and register "actions" -- simple
functions that get called with a list of objects selected on the change list
page.

If you look at any change list in the admin, you'll see this feature in
action; Django ships with a "delete selected objects" action available to all
models. For example, here's the user module from Django's built-in
:mod:`django.contrib.auth` app:

.. image:: _images/user_actions.png

.. warning::

    The "delete selected objects" action uses :meth:`QuerySet.delete()
    <django.db.models.QuerySet.delete>` for efficiency reasons, which has an
    important caveat: your model's ``delete()`` method will not be called.
    
    If you wish to override this behavior, simply write a custom action which
    accomplishes deletion in your preferred manner -- for example, by calling
    ``Model.delete()`` for each of the selected items.
    
    For more background on bulk deletion, see the documentation on :ref:`object
    deletion <topics-db-queries-delete>`.

Read on to find out how to add your own actions to this list.

Writing actions
===============

The easiest way to explain actions is by example, so let's dive in.

A common use case for admin actions is the bulk updating of a model. Imagine a
simple news application with an ``Article`` model::

    from django.db import models

    STATUS_CHOICES = (
        ('d', 'Draft'),
        ('p', 'Published'),
        ('w', 'Withdrawn'),
    )

    class Article(models.Model):
        title = models.CharField(max_length=100)
        body = models.TextField()
        status = models.CharField(max_length=1, choices=STATUS_CHOICES)
    
        def __unicode__(self):
            return self.title
        
A common task we might perform with a model like this is to update an
article's status from "draft" to "published". We could easily do this in the
admin one article at a time, but if we wanted to bulk-publish a group of
articles, it'd be tedious. So, let's write an action that lets us change an
article's status to "published."

Writing action functions
------------------------

First, we'll need to write a function that gets called when the action is
trigged from the admin. Action functions are just regular functions that take
three arguments: 
    
    * The current :class:`ModelAdmin`
    * An :class:`~django.http.HttpRequest` representing the current request,
    * A :class:`~django.db.models.QuerySet` containing the set of objects
      selected by the user.

Our publish-these-articles function won't need the :class:`ModelAdmin` or the
request object, but we will use the queryset::

    def make_published(modeladmin, request, queryset):
        queryset.update(status='p')
        
.. note::

    For the best performance, we're using the queryset's :ref:`update method
    <topics-db-queries-update>`. Other types of actions might need to deal
    with each object individually; in these cases we'd just iterate over the
    queryset::
    
        for obj in queryset:
            do_something_with(obj)
            
That's actually all there is to writing an action! However, we'll take one
more optional-but-useful step and give the action a "nice" title in the admin.
By default, this action would appear in the action list as "Make published" --
the function name, with underscores replaced by spaces. That's fine, but we
can provide a better, more human-friendly name by giving the
``make_published`` function a ``short_description`` attribute::

    def make_published(modeladmin, request, queryset):
        queryset.update(status='p')
    make_published.short_description = "Mark selected stories as published"
    
.. note::

    This might look familiar; the admin's ``list_display`` option uses the
    same technique to provide human-readable descriptions for callback
    functions registered there, too.
    
Adding actions to the :class:`ModelAdmin`
-----------------------------------------

Next, we'll need to inform our :class:`ModelAdmin` of the action. This works
just like any other configuration option. So, the complete ``admin.py`` with
the action and its registration would look like::

    from django.contrib import admin
    from myapp.models import Article

    def make_published(modeladmin, request, queryset):
        queryset.update(status='p')
    make_published.short_description = "Mark selected stories as published"

    class ArticleAdmin(admin.ModelAdmin):
        list_display = ['title', 'status']
        ordering = ['title']
        actions = [make_published]

    admin.site.register(Article, ArticleAdmin)
    
That code will give us an admin change list that looks something like this:

.. image:: _images/article_actions.png
    
That's really all there is to it! If you're itching to write your own actions,
you now know enough to get started. The rest of this document just covers more
advanced techniques.

Advanced action techniques
==========================

There's a couple of extra options and possibilities you can exploit for more
advanced options.

Actions as :class:`ModelAdmin` methods
--------------------------------------

The example above shows the ``make_published`` action defined as a simple
function. That's perfectly fine, but it's not perfect from a code design point
of view: since the action is tightly coupled to the ``Article`` object, it
makes sense to hook the action to the ``ArticleAdmin`` object itself.

That's easy enough to do::

    class ArticleAdmin(admin.ModelAdmin):
        ...
        
        actions = ['make_published']

        def make_published(self, request, queryset):
            queryset.update(status='p')
        make_published.short_description = "Mark selected stories as published"
        
Notice first that we've moved ``make_published`` into a method and renamed the
`modeladmin` parameter to `self`, and second that we've now put the string
``'make_published'`` in ``actions`` instead of a direct function reference. This
tells the :class:`ModelAdmin` to look up the action as a method.

Defining actions as methods gives the action more straightforward, idiomatic
access to the :class:`ModelAdmin` itself, allowing the action to call any of the
methods provided by the admin.

.. _custom-admin-action:

For example, we can use ``self`` to flash a message to the user informing her
that the action was successful::

    class ArticleAdmin(admin.ModelAdmin):
        ...

        def make_published(self, request, queryset):
            rows_updated = queryset.update(status='p')
            if rows_updated == 1:
                message_bit = "1 story was"
            else:
                message_bit = "%s stories were" % rows_updated
            self.message_user(request, "%s successfully marked as published." % message_bit)

This make the action match what the admin itself does after successfully
performing an action:

.. image:: _images/article_actions_message.png
    
Actions that provide intermediate pages
---------------------------------------

By default, after an action is performed the user is simply redirected back
to the original change list page. However, some actions, especially more
complex ones, will need to return intermediate pages. For example, the
built-in delete action asks for confirmation before deleting the selected
objects.

To provide an intermediary page, simply return an
:class:`~django.http.HttpResponse` (or subclass) from your action. For
example, you might write a simple export function that uses Django's
:doc:`serialization functions </topics/serialization>` to dump some selected
objects as JSON::

    from django.http import HttpResponse
    from django.core import serializers

    def export_as_json(modeladmin, request, queryset):
        response = HttpResponse(mimetype="text/javascript")
        serializers.serialize("json", queryset, stream=response)
        return response

Generally, something like the above isn't considered a great idea. Most of the
time, the best practice will be to return an
:class:`~django.http.HttpResponseRedirect` and redirect the user to a view
you've written, passing the list of selected objects in the GET query string.
This allows you to provide complex interaction logic on the intermediary
pages. For example, if you wanted to provide a more complete export function,
you'd want to let the user choose a format, and possibly a list of fields to
include in the export. The best thing to do would be to write a small action
that simply redirects to your custom export view::

    from django.contrib import admin
    from django.contrib.contenttypes.models import ContentType
    from django.http import HttpResponseRedirect
    
    def export_selected_objects(modeladmin, request, queryset):
        selected = request.POST.getlist(admin.ACTION_CHECKBOX_NAME)
        ct = ContentType.objects.get_for_model(queryset.model)
        return HttpResponseRedirect("/export/?ct=%s&ids=%s" % (ct.pk, ",".join(selected)))

As you can see, the action is the simple part; all the complex logic would
belong in your export view. This would need to deal with objects of any type,
hence the business with the ``ContentType``.

Writing this view is left as an exercise to the reader.

.. _adminsite-actions:

Making actions available site-wide
----------------------------------

.. method:: AdminSite.add_action(action[, name])

    Some actions are best if they're made available to *any* object in the admin
    site -- the export action defined above would be a good candidate. You can
    make an action globally available using :meth:`AdminSite.add_action()`. For
    example::

        from django.contrib import admin
        
        admin.site.add_action(export_selected_objects)

    This makes the `export_selected_objects` action globally available as an
    action named `"export_selected_objects"`. You can explicitly give the action
    a name -- good if you later want to programatically :ref:`remove the action
    <disabling-admin-actions>` -- by passing a second argument to
    :meth:`AdminSite.add_action()`::
    
        admin.site.add_action(export_selected_objects, 'export_selected')

.. _disabling-admin-actions:

Disabling actions
-----------------

Sometimes you need to disable certain actions -- especially those
:ref:`registered site-wide <adminsite-actions>` -- for particular objects.
There's a few ways you can disable actions:

Disabling a site-wide action
~~~~~~~~~~~~~~~~~~~~~~~~~~~~

.. method:: AdminSite.disable_action(name)

    If you need to disable a :ref:`site-wide action <adminsite-actions>` you can
    call :meth:`AdminSite.disable_action()`.
    
    For example, you can use this method to remove the built-in "delete selected
    objects" action::
    
        admin.site.disable_action('delete_selected')
        
    Once you've done the above, that action will no longer be available
    site-wide.
    
    If, however, you need to re-enable a globally-disabled action for one
    particular model, simply list it explicitly in your ``ModelAdmin.actions``
    list::
    
        # Globally disable delete selected
        admin.site.disable_action('delete_selected')
        
        # This ModelAdmin will not have delete_selected available
        class SomeModelAdmin(admin.ModelAdmin):
            actions = ['some_other_action']
            ...
            
        # This one will
        class AnotherModelAdmin(admin.ModelAdmin):
            actions = ['delete_selected', 'a_third_action']
            ...
            

Disabling all actions for a particular :class:`ModelAdmin`
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

If you want *no* bulk actions available for a given :class:`ModelAdmin`, simply
set :attr:`ModelAdmin.actions` to ``None``::

    class MyModelAdmin(admin.ModelAdmin):
        actions = None
        
This tells the :class:`ModelAdmin` to not display or allow any actions,
including any :ref:`site-wide actions <adminsite-actions>`.

Conditionally enabling or disabling actions
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

.. method:: ModelAdmin.get_actions(request)

    Finally, you can conditionally enable or disable actions on a per-request 
    (and hence per-user basis) by overriding :meth:`ModelAdmin.get_actions`.

    This returns a dictionary of actions allowed. The keys are action names, and
    the values are ``(function, name, short_description)`` tuples.

    Most of the time you'll use this method to conditionally remove actions from
    the list gathered by the superclass. For example, if I only wanted users
    whose names begin with 'J' to be able to delete objects in bulk, I could do
    the following::
    
        class MyModelAdmin(admin.ModelAdmin):
            ...
            
            def get_actions(self, request):
                actions = super(MyModelAdmin, self).get_actions(request)
                if request.user.username[0].upper() != 'J':
                    del actions['delete_selected']
                return actions