==============================

The syndication feed framework

==============================

Django comes with a high-level syndication-feed-generating framework that makes

creating RSS_ and Atom_ feeds easy.

To create any syndication feed, all you have to do is write a short Python

class. You can create as many feeds as you want.

Django also comes with a lower-level feed-generating API. Use this if you want

to generate feeds outside of a Web context, or in some other lower-level way.

.. _RSS: http://www.whatisrss.com/

.. _Atom: http://www.atomenabled.org/

The high-level framework

========================

Overview

--------

The high-level feed-generating framework is a view that's hooked to ``/feeds/``

by default. Django uses the remainder of the URL (everything after ``/feeds/``)

to determine which feed to output.

To create a feed, just write a ``Feed`` class and point to it in your URLconf_.

.. _URLconf: ../url_dispatch/

Initialization

--------------

To activate syndication feeds on your Django site, add this line to your

URLconf_::

    (r'^feeds/(?P<url>.*)/$', 'django.contrib.syndication.views.feed', {'feed_dict': feeds}),

This tells Django to use the RSS framework to handle all URLs starting with

``"feeds/"``. (You can change that ``"feeds/"`` prefix to fit your own needs.)

This URLconf line has an extra argument: ``{'feed_dict': feeds}``. Use this

extra argument to pass the syndication framework the feeds that should be

published under that URL.

Specifically, ``feed_dict`` should be a dictionary that maps a feed's slug

(short URL label) to its ``Feed`` class.

You can define the ``feed_dict`` in the URLconf itself. Here's a full example

URLconf::

    from django.conf.urls.defaults import *

    from myproject.feeds import LatestEntries, LatestEntriesByCategory

    feeds = {

        'latest': LatestEntries,

        'categories': LatestEntriesByCategory,

    }

    urlpatterns = patterns('',

        # ...

        (r'^feeds/(?P<url>.*)/$', 'django.contrib.syndication.views.feed',

            {'feed_dict': feeds}),

        # ...

    )

The above example registers two feeds:

    * The feed represented by ``LatestEntries`` will live at ``feeds/latest/``.

    * The feed represented by ``LatestEntriesByCategory`` will live at

      ``feeds/categories/``.

Once that's set up, you just need to define the ``Feed`` classes themselves.

.. _URLconf: ../url_dispatch/

.. _settings file: ../settings/

Feed classes

------------

A ``Feed`` class is a simple Python class that represents a syndication feed.

A feed can be simple (e.g., a "site news" feed, or a basic feed displaying

the latest entries of a blog) or more complex (e.g., a feed displaying all the

blog entries in a particular category, where the category is variable).

``Feed`` classes must subclass ``django.contrib.syndication.feeds.Feed``. They

can live anywhere in your codebase.

A simple example

----------------

This simple example, taken from `chicagocrime.org`_, describes a feed of the

latest five news items::

    from django.contrib.syndication.feeds import Feed

    from chicagocrime.models import NewsItem

    class LatestEntries(Feed):

        title = "Chicagocrime.org site news"

        link = "/sitenews/"

        description = "Updates on changes and additions to chicagocrime.org."

        def items(self):

            return NewsItem.objects.order_by('-pub_date')[:5]

Note:

    * The class subclasses ``django.contrib.syndication.feeds.Feed``.

    * ``title``, ``link`` and ``description`` correspond to the standard

      RSS ``<title>``, ``<link>`` and ``<description>`` elements, respectively.

    * ``items()`` is, simply, a method that returns a list of objects that

      should be included in the feed as ``<item>`` elements. Although this

      example returns ``NewsItem`` objects using Django's

      `object-relational mapper`_, ``items()`` doesn't have to return model

      instances. Although you get a few bits of functionality "for free" by

      using Django models, ``items()`` can return any type of object you want.

One thing's left to do. In an RSS feed, each ``<item>`` has a ``<title>``,

``<link>`` and ``<description>``. We need to tell the framework what data to

put into those elements.

    * To specify the contents of ``<title>`` and ``<description>``, create

      `Django templates`_ called ``feeds/latest_title.html`` and

      ``feeds/latest_description.html``, where ``latest`` is the ``slug``

      specified in the URLconf for the given feed. Note the ``.html`` extension

      is required. The RSS system renders that template for each item, passing

      it two template context variables:

          * ``{{ obj }}`` -- The current object (one of whichever objects you

            returned in ``items()``).

          * ``{{ site }}`` -- A ``django.models.core.sites.Site`` object

            representing the current site. This is useful for

            ``{{ site.domain }}`` or ``{{ site.name }}``.

      If you don't create a template for either the title or description, the

      framework will use the template ``"{{ obj }}"`` by default -- that is,

      the normal string representation of the object. You can also change the

      names of these two templates by specifying ``title_template`` and

      ``description_template`` as attributes of your ``Feed`` class.

    * To specify the contents of ``<link>``, you have two options. For each

      item in ``items()``, Django first tries executing a

      ``get_absolute_url()`` method on that object. If that method doesn't

      exist, it tries calling a method ``item_link()`` in the ``Feed`` class,

      passing it a single parameter, ``item``, which is the object itself.

      Both ``get_absolute_url()`` and ``item_link()`` should return the item's

      URL as a normal Python string.

    * For the LatestEntries example above, we could have very simple feed templates:

          * latest_title.html::

             {{ obj.title }}

          * latest_description.html::

             {{ obj.description }}

.. _chicagocrime.org: http://www.chicagocrime.org/

.. _object-relational mapper: ../db_api/

.. _Django templates: ../templates/

A complex example

-----------------

The framework also supports more complex feeds, via parameters.

For example, `chicagocrime.org`_ offers an RSS feed of recent crimes for every

police beat in Chicago. It'd be silly to create a separate ``Feed`` class for

each police beat; that would violate the `DRY principle`_ and would couple data

to programming logic. Instead, the syndication framework lets you make generic

feeds that output items based on information in the feed's URL.

On chicagocrime.org, the police-beat feeds are accessible via URLs like this:

    * ``/rss/beats/0613/`` -- Returns recent crimes for beat 0613.

    * ``/rss/beats/1424/`` -- Returns recent crimes for beat 1424.

The slug here is ``"beats"``. The syndication framework sees the extra URL bits

after the slug -- ``0613`` and ``1424`` -- and gives you a hook to tell it what

those URL bits mean, and how they should influence which items get published in

the feed.

An example makes this clear. Here's the code for these beat-specific feeds::

    class BeatFeed(Feed):

        def get_object(self, bits):

            # In case of "/rss/beats/0613/foo/bar/baz/", or other such clutter,

            # check that bits has only one member.

            if len(bits) != 1:

                raise ObjectDoesNotExist

            return Beat.objects.get(beat__exact=bits[0])

        def title(self, obj):

            return "Chicagocrime.org: Crimes for beat %s" % obj.beat

        def link(self, obj):

            return obj.get_absolute_url()

        def description(self, obj):

            return "Crimes recently reported in police beat %s" % obj.beat

        def items(self, obj):

            return Crime.objects.filter(beat__id__exact=obj.id).order_by('-crime_date')[:30]

Here's the basic algorithm the RSS framework follows, given this class and a

request to the URL ``/rss/beats/0613/``:

    * The framework gets the URL ``/rss/beats/0613/`` and notices there's

      an extra bit of URL after the slug. It splits that remaining string by

      the slash character (``"/"``) and calls the ``Feed`` class'

      ``get_object()`` method, passing it the bits. In this case, bits is

      ``['0613']``. For a request to ``/rss/beats/0613/foo/bar/``, bits would

      be ``['0613', 'foo', 'bar']``.

    * ``get_object()`` is responsible for retrieving the given beat, from the

      given ``bits``. In this case, it uses the Django database API to retrieve

      the beat. Note that ``get_object()`` should raise

      ``django.core.exceptions.ObjectDoesNotExist`` if given invalid

      parameters. There's no ``try``/``except`` around the

      ``Beat.objects.get()`` call, because it's not necessary; that function

      raises ``Beat.DoesNotExist`` on failure, and ``Beat.DoesNotExist`` is a

      subclass of ``ObjectDoesNotExist``. Raising ``ObjectDoesNotExist`` in

      ``get_object()`` tells Django to produce a 404 error for that request.

    * To generate the feed's ``<title>``, ``<link>`` and ``<description>``,

      Django uses the ``title()``, ``link()`` and ``description()`` methods. In

      the previous example, they were simple string class attributes, but this

      example illustrates that they can be either strings *or* methods. For

      each of ``title``, ``link`` and ``description``, Django follows this

      algorithm:

          * First, it tries to call a method, passing the ``obj`` argument, where

            ``obj`` is the object returned by ``get_object()``.

          * Failing that, it tries to call a method with no arguments.

          * Failing that, it uses the class attribute.

    * Finally, note that ``items()`` in this example also takes the ``obj``

      argument. The algorithm for ``items`` is the same as described in the

      previous step -- first, it tries ``items(obj)``, then ``items()``, then

      finally an ``items`` class attribute (which should be a list).

The ``ExampleFeed`` class below gives full documentation on methods and

attributes of ``Feed`` classes.

.. _DRY principle: http://c2.com/cgi/wiki?DontRepeatYourself

Specifying the type of feed

---------------------------

By default, feeds produced in this framework use RSS 2.0.

To change that, add a ``feed_type`` attribute to your ``Feed`` class, like so::

    from django.utils.feedgenerator import Atom1Feed

    class MyFeed(Feed):

        feed_type = Atom1Feed

Note that you set ``feed_type`` to a class object, not an instance.

Currently available feed types are:

    * ``django.utils.feedgenerator.Rss201rev2Feed`` (RSS 2.01. Default.)

    * ``django.utils.feedgenerator.RssUserland091Feed`` (RSS 0.91.)

    * ``django.utils.feedgenerator.Atom1Feed`` (Atom 1.0.)

Enclosures

----------

To specify enclosures, such as those used in creating podcast feeds, use the

``item_enclosure_url``, ``item_enclosure_length`` and

``item_enclosure_mime_type`` hooks. See the ``ExampleFeed`` class below for

usage examples.

Language

--------

Feeds created by the syndication framework automatically include the

appropriate ``<language>`` tag (RSS 2.0) or ``xml:lang`` attribute (Atom). This

comes directly from your `LANGUAGE_CODE setting`_.

.. _LANGUAGE_CODE setting: ../settings/#language-code

URLs

----

The ``link`` method/attribute can return either an absolute URL (e.g.

``"/blog/"``) or a URL with the fully-qualified domain and protocol (e.g.

``"http://www.example.com/blog/"``). If ``link`` doesn't return the domain,

the syndication framework will insert the domain of the current site, according

to your `SITE_ID setting`_.

Atom feeds require a ``<link rel="self">`` that defines the feed's current

location. The syndication framework populates this automatically, using the

domain of the current site according to the SITE_ID setting.

.. _SITE_ID setting: ../settings/#site-id

Publishing Atom and RSS feeds in tandem

---------------------------------------

Some developers like to make available both Atom *and* RSS versions of their

feeds. That's easy to do with Django: Just create a subclass of your ``feed``

class and set the ``feed_type`` to something different. Then update your

URLconf to add the extra versions.

Here's a full example::

    from django.contrib.syndication.feeds import Feed

    from chicagocrime.models import NewsItem

    from django.utils.feedgenerator import Atom1Feed

    class RssSiteNewsFeed(Feed):

        title = "Chicagocrime.org site news"

        link = "/sitenews/"

        description = "Updates on changes and additions to chicagocrime.org."

        def items(self):

            return NewsItem.objects.order_by('-pub_date')[:5]

    class AtomSiteNewsFeed(RssSiteNewsFeed):

        feed_type = Atom1Feed

And the accompanying URLconf::

    from django.conf.urls.defaults import *

    from myproject.feeds import RssSiteNewsFeed, AtomSiteNewsFeed

    feeds = {

        'rss': RssSiteNewsFeed,

        'atom': AtomSiteNewsFeed,

    }

    urlpatterns = patterns('',

        # ...

        (r'^feeds/(?P<url>.*)/$', 'django.contrib.syndication.views.feed',

            {'feed_dict': feeds}),

        # ...

    )

Feed class reference

--------------------

This example illustrates all possible attributes and methods for a ``Feed`` class::

    from django.contrib.syndication.feeds import Feed

    from django.utils import feedgenerator

    class ExampleFeed(Feed):

        # FEED TYPE -- Optional. This should be a class that subclasses

        # django.utils.feedgenerator.SyndicationFeed. This designates which

        # type of feed this should be: RSS 2.0, Atom 1.0, etc.

        # If you don't specify feed_type, your feed will be RSS 2.0.

        # This should be a class, not an instance of the class.

        feed_type = feedgenerator.Rss201rev2Feed

        # TEMPLATE NAMES -- Optional. These should be strings representing

        # names of Django templates that the system should use in rendering the

        # title and description of your feed items. Both are optional.

        # If you don't specify one, or either, Django will use the template

        # 'feeds/SLUG_title.html' and 'feeds/SLUG_description.html', where SLUG

        # is the slug you specify in the URL.

        title_template = None

        description_template = None

        # TITLE -- One of the following three is required. The framework looks

        # for them in this order.

        def title(self, obj):

            """

            Takes the object returned by get_object() and returns the feed's

            title as a normal Python string.

            """

        def title(self):

            """

            Returns the feed's title as a normal Python string.

            """

        title = 'foo' # Hard-coded title.

        # LINK -- One of the following three is required. The framework looks

        # for them in this order.

        def link(self, obj):

            """

            Takes the object returned by get_object() and returns the feed's

            link as a normal Python string.

            """

        def link(self):

            """

            Returns the feed's link as a normal Python string.

            """

        link = '/foo/bar/' # Hard-coded link.

        # DESCRIPTION -- One of the following three is required. The framework

        # looks for them in this order.

        def description(self, obj):

            """

            Takes the object returned by get_object() and returns the feed's

            description as a normal Python string.

            """

        def description(self):

            """

            Returns the feed's description as a normal Python string.

            """

        description = 'Foo bar baz.' # Hard-coded description.

        # AUTHOR NAME --One of the following three is optional. The framework

        # looks for them in this order.

        def author_name(self, obj):

            """

            Takes the object returned by get_object() and returns the feed's

            author's name as a normal Python string.

            """

        def author_name(self):

            """

            Returns the feed's author's name as a normal Python string.

            """

        author_name = 'Sally Smith' # Hard-coded author name.

        # AUTHOR E-MAIL --One of the following three is optional. The framework

        # looks for them in this order.

        def author_email(self, obj):

            """

            Takes the object returned by get_object() and returns the feed's

            author's e-mail as a normal Python string.

            """

        def author_email(self):

            """

            Returns the feed's author's e-mail as a normal Python string.

            """

        author_email = 'test@example.com' # Hard-coded author e-mail.

        # AUTHOR LINK --One of the following three is optional. The framework

        # looks for them in this order. In each case, the URL should include

        # the "http://" and domain name.

        def author_link(self, obj):

            """

            Takes the object returned by get_object() and returns the feed's

            author's URL as a normal Python string.

            """

        def author_link(self):

            """

            Returns the feed's author's URL as a normal Python string.

            """

        author_link = 'http://www.example.com/' # Hard-coded author URL.

        # CATEGORIES -- One of the following three is optional. The framework

        # looks for them in this order. In each case, the method/attribute

        # should return an iterable object that returns strings.

        def categories(self, obj):

            """

            Takes the object returned by get_object() and returns the feed's

            categories as iterable over strings.

            """

        def categories(self):

            """

            Returns the feed's categories as iterable over strings.

            """

        categories = ("python", "django") # Hard-coded list of categories.

        # COPYRIGHT NOTICE -- One of the following three is optional. The

        # framework looks for them in this order.

        def copyright(self, obj):

            """

            Takes the object returned by get_object() and returns the feed's

            copyright notice as a normal Python string.

            """

        def copyright(self):

            """

            Returns the feed's copyright notice as a normal Python string.

            """

        copyright = 'Copyright (c) 2007, Sally Smith' # Hard-coded copyright notice.

        # ITEMS -- One of the following three is required. The framework looks

        # for them in this order.

        def items(self, obj):

            """

            Takes the object returned by get_object() and returns a list of

            items to publish in this feed.

            """

        def items(self):

            """

            Returns a list of items to publish in this feed.

            """

        items = ('Item 1', 'Item 2') # Hard-coded items.

        # GET_OBJECT -- This is required for feeds that publish different data

        # for different URL parameters. (See "A complex example" above.)

        def get_object(self, bits):

            """

            Takes a list of strings gleaned from the URL and returns an object

            represented by this feed. Raises

            django.core.exceptions.ObjectDoesNotExist on error.

            """

        # ITEM LINK -- One of these three is required. The framework looks for

        # them in this order.

        # First, the framework tries the get_absolute_url() method on each item

        # returned by items(). Failing that, it tries these two methods:

        def item_link(self, item):