OData queries and types other than IQueryable in ASP.NET Web API

Question

I am building an ASP.NET Web API application that returns an Atom or an RSS feed. To do this, it builds a System.ServiceModel.Syndication.SyndicationFeed and a custom MediaTypeFormatter is responsible for handling the HTTP Accept Header, converting the SyndicationFeed to either an Atom10FeedFormatter or an Rss20FeedFormatter , and streaming the result to the response stream. So far, so good.

My controller looks something like this:

public class FeedController : ApiController
    {
        public HttpResponseMessage Get()
        {
            FeedRepository feedRepository = new FeedRepository();
            HttpResponseMessage<SyndicationFeed> successResponseMessage = new HttpResponseMessage<SyndicationFeed>(feedRepository.GetSyndicationFeed());
            return successResponseMessage;
        }
    }

What I would like to do is make use of the built-in OData querying to filter my feed, but changing the return type of the Get() method to IQueryable<SyndicationFeed> obviously will not work since a SyndicationFeed does not implement IQueryable .

Is there a way to use the built in OData querying on the IEnumerable<SyndicationItem> property on the SyndicationFeed ?

Answer 1

This question is no longer relevant, since Microsoft remove the rudimentary support for OData querying that was in the Beta build of Web API.

A future version will include more complete OData support. There is an early build of this available via CodePlex and NuGet and there are more details here: http://blogs.msdn.com/b/alexj/archive/2012/08/15/odata-support-in-asp-net-web-api.aspx

Answer 2

The System.Linq namespace provides an extension method named AsQueryable to the IEnumerable interface. Your code would look along the lines of this:

public class FeedController : ApiController
{
    public IQueryable<SyndicationFeed> Get()
    {
        FeedRepository feedRepository = new FeedRepository();

        //TODO: Make sure your property handles empty/null results:
        return feedRepository.GetSyndicationFeed()
                   .YourEnumerableProperty.AsQueryable();
    }
}

Answer 3

You don't have to return IQuerable from controller when working with OData. Check "Invoking Query Options Directly" section at https://docs.microsoft.com/en-us/aspnet/web-api/overview/odata-support-in-aspnet-web-api/supporting-odata-query-options

For your case it will looks like:

public SyndicationFeed Get(ODataQueryOptions<SyndicationItem> opts)
{
    var settings = new ODataValidationSettings();

    opts.Validate(settings);

    SyndicationFeed result = feedRepository.GetSyndicationFeed();

    result.Items = opts.ApplyTo(result.Items.AsQuerable()).ToArray();

    return result;
}