Dealing with List Feeds

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Dealing with List Feeds

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Recently, I received an interesting customer question I thought I would share.

A web developer presented me with the following scenario: his web application lets users create and manage a list of items, and this list is exposed as a feed so users can be updated when it changes. However, after the user deletes an item using the web application, that item is still present in the feed view of the RSS aggregator. Since the feed is supposed to correctly reflect the state of the user’s item list, this was a problem.

Unfortunately, the desired behavior doesn’t quite work with established feed usage. A majority of feeds expose only a small number of most recent items and older items periodically get aged out. But you wouldn’t want to miss posts from your favorite blog or news feed just because you went on vacation and those posts are no longer in a feed! This is why the Windows RSS Platform stores all the items until the user-controllable feed item storage limit is reached (200 items by default).

Fortunately, I had good news for the customer – there is a very simple solution to his problem!
IE7 and the Windows RSS Platform fully support feeds that contain a complete ordered list of items. All you need to do to make your feed a list is add one simple extension under the <channel> node (or for Atom feeds, under the <feed> node):

<channel>
  <cf:treatAs xmlns:cf="http://www.microsoft.com/schemas/rss/core/2005">list</cf:treatAs>

</channel>

The “treatAs” extension is part of the Simple List Extensions (SLE). These are the feed extensions we designed with the exact purpose of exposing ordered lists of items in a feed, and made available to everyone under the Creative Commons license. SLE follow the feed extensions rules so they work in combination with other RSS extensions and the resulting feed can be read with any feed reader. You can find the full explanation with samples and pointers to live list feeds in one of our earlier posts on the RSS team blog here, or get a hands-on experience with the recently posted RSS lab at the MIX University.

Needless to say, the customer was pretty happy with how easy this was.

If you haven’t looked at the SLE already, this might be a great time to do so. They might just be the perfect answer for your scenario.

Miladin Pavlicic
Senior Developer

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