.. _ref-contrib-admin-actions:

=============
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
    
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        ('w', 'Withdrawn'),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
two arguments: an :class:`~django.http.HttpRequest` representing the current
request, and a :class:`~django.db.models.QuerySet` containing the set of
objects selected by the user. Our publish-these-articles function won't need
the request object, but we will use the queryset::

    def make_published(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(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(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 (remembering to
add the ``self`` argument!), 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 is especially nice because it gives the action
access to the :class:`ModelAdmin` itself, allowing the action to call any of
the methods provided by the admin.

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
the 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
:ref:`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(request, queryset):
        response = HttpResponse(mimetype="text/javascript")
        serialize.serialize(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(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.

Making actions available globally
---------------------------------

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

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