Support GeoRSS in syndication of Geographic Models

There's no need to limit this to only GeoDjango. All that's needed is to add item_location to the base SyndicationFeed? that adds a location (tuple?) to item, then change the syndictation-types to spit out a <georss:point>-line if item has a location.

Then pepole would override item_location in the exact same way they already do for links, authors, categories etc.

Now if growing feeds by adding extra xml-tags becomes common, there should probably be a generic way of adding such tags, especially if they are as undemanding as georss.

I looked at this a bit tonight (because I want to generate some GeoRSS feeds)... comments are below. Mostly referring to Atom but similar concepts apply to RSS - noted in (brackets):

• creating a subclass of django.contrib.syndication.feeds.Feed with item_location and location parameters won't be a problem to extract a geometry field from a model
• the problem comes with respect to django.utils.feedgenerator.SyndicationFeed:
  • we want to add a <georss:where> clause to the feed(channel), each entry(item), or both.
  • we need to add the georss namespace declaration to <feed> (<channel>)
  • there are no hooks for extending either the feed or the entry, which means we'd have to reimplement/duplicate the entire write() and write_items() for each feed format. :(

Ok, so that's not gonna happen.

Extensions I think should be added to SyndicationFeed & its implementations to allow us to GeoRSS-ify stuff:

• SyndicationFeed.__init__() and SyndicationFeed.add_item() should take kwargs which are added into the feed/item dictionaries respectively.
• extra_attrs(): Add attributes to the root feed(channel) element. eg. xmlns:georss="http://...". Returns a dictionary. Called from write()
• extras(handler): Add elements within the feed(channel) element. eg. a <georss:where> for the feed. Called from write()
• item_extra_attrs(item): Add attributes to the entry(item) elements (called once for each item). Returns a dictionary. Called from write_items()
• item_extras(handler, item): Add elements within the entry(item) elements (called once for each item). Would be where the georss would be added. Called from write_items()

Once we have those hooks we can do a mixin with each of the existing SyndicationFeed? implementations and a GeoRSS implementation that knows how to turn a geometry object into a suitable GeoRSS clause. It would not just do georss then, but could also do media: or any other extensions. Thats quite a sizeable set of changes though, so I guess we need to bring it up on django-dev, and who knows whether it'll get through pre-1.0. I think those hooks make things much more flexible without needing to go to the lengths of rewriting the whole framework.

See also:

• #3569
• http://code.google.com/p/django-atompub/wiki/UserGuide

Probably should be another ticket, but I thought i'd get some initial feedback first.

(In [8310]) Added a couple of extra syndication tests, and generally sanitized the existing ones. Refs #6547.

(In [8311]) Added a number of callbacks to SyndicationFeed? for adding custom attributes and elements to feeds. Refs #6547.

OK, Justin, it's all you now.

Now that [8311] and [8331] are in, there's no reason this needs to block the beta.

Awesome Jacob, I'll work up a patch for the GeoRSS bit :)

Patch for GeoRSS; also includes some internal changes to Feed

In my patch I added django.contrib.gis.feeds.Feed, which has support for simple GeoRSS. You may specify a geometry element on the entire feed by defining a geometry function; similarly, geometries in the feed may be specified by item_geometry method -- both should return a WGS84 (GEOS|OGR)Geometry.

Some big internal changes to the original Feed class, specifically abstracting a lot to the (now) subclassable get_feed_kwargs and get_item_kwargs methods. Tests pass, but I want some input on whether it's OK to make some of those variables class-wide (e.g., self.current_site, and the templates). This makes subclassing Feed easier, granting access to the __get_dynamic_attr magic.

Version 2; uses W3C Geo for RSS points.

W3C Geo is no longer default for points on RSS feeds, but is now its own subclass.

Less intrusive patch to contrib.syndication.

(In [8414]) Fixed #6547, added support for GeoRSS feeds in django.contrib.gis.feeds; added the feed_extra_kwargs and item_extra_kwargs to the Feed baseclass so that it's possible for subclasses to add dynamic attributes.