RSS 2 / Atom 1 Feeds

.NET 3.5 adds a WebHttp WCF binding and Synidication support. I haven’t tried anything with syndication yet. Now seemed like a good time.

The DvdFriend home page shows the most recent 50 ratings/reviews. I’ve received more than one request to make that, and comments, available as feeds. I started with the recent activity.
Setting it up as a WCF service was pretty easy, though I’ll probably end up dropping it. I’ll probably just expose it as SYNDICATION.aspx or something. We’ll see. Regardless, doing it as a WCF service was a good experience.

Once I had a test feed going, it was time to populate it with the actual data. I thought LINQ would be the way to go. I already have a static method that returns a list of the recent reviews as a data table. I thought I’d just write a linq query against that data table. No dice. LINQ doesn’t work on data tables. Swell. (Well, not really).

I wrote a generic wrapper class to make things enumerable for linq. (Is this the best solution? I don’t know. But it works.)

NOTE: Changed this code. See notes at the bottom. (Changed GetEnumerator to return _items.GetEnumerator rather than yield through it itself)
Next, I had to write a Linq query that would return a List. In the process, I had to explore some of the properties and methods to see what was what. I set the basic stuff, but there were 2 things that I wanted to set, but couldn’t during initialization:

– The author. SyndicationItem.Authors is a List(), so you don’t initialize it. You have to add to the existing list.

– The item link. At first, I figured this would be BASEURI, but it wasn’t. You have to call item.AddPermaLink(new Uri(“…”)). Its a method; can’t call it during initialization.

For author, I could loop through all the items after the initial query and update the individual items from the datatable. But, not interested. That didn’t sound like a very good solution. I only want to hit the datatable once and be done with it. PermLink would require a loop too, but that’s based on ID which is already a property of SyndicationItem, so no problem there.

I solved the author issue by creating a subclass of SynidcationItem called AllardWorksSyndicationItem. I added a property called AUTHOR, so that I can save the information during load. Then, I can loop through and update the AUTHORS collection without having to bother the data table.
The Linq query now returns a List. After the query, I loop through the items and create the permalink (based on the ID, which I already have), and I add the value of the new AUTHOR property to the existing AUTHORS property.

But wait. There’s more. The SyndicationFeed object has a property called Items. You set it to a IEnumerable of SyndicationObject, not IEnumerable of AllardWorksSyndicationItem. The list needs to be converted. I achieved this by another Linq query which does the cast
Then, you return a formatter for the type of feed (I chose atom), and that’s a wrap for tonight.

Final Code

Rendered in IE

Coming soon!
I revisited some of this.
I realized that LinqWrapper.GetEnumerator was silly, because DataRowCollection is already IEnumerable. All you have to do it
return (IEnumerator)_items.GetEnumerator();
rather than yield through it yourself.
Then I was bothered by the fact that DataRowCollection is already IEnumerable, so why do I need this stupid wrapper class?
The reason is that DataRowCollection is IEnumerable. Linq requires IEnumerable, so the wrapper converts it. I tried finding other

Leave a Reply

Please log in using one of these methods to post your comment: Logo

You are commenting using your account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )


Connecting to %s

%d bloggers like this: