.Net WebApi OData Actions that return an Queryable

Question

I want to achieve something close to the RateProduct action described in: http://www.asp.net/web-api/overview/odata-support-in-aspnet-web-api/odata-actions

In that tutorial it is defined as:

[HttpPost]
public int RateProduct([FromODataUri] int key, ODataActionParameters parameters) 
{ 
    // ...
}

ODataModelBuilder modelBuilder = new ODataConventionModelBuilder();
modelBuilder.EntitySet<Product>("Products");

// New Code
ActionConfiguration rateProduct = modelBuilder.Entity<Product>().Action("RateProduct");
rateProduct.Parameter<int>("Rating");
rateProduct.Returns<int>();

However, I have the use case of a Location entity that is smart enough to return other Locations within a certain radius around it. It should roughly be like this:

[HttpPost]
public IQueryable<Location> GetLocationsWithinRadius([FromODataUri] int key, ODataActionParameters parameters) 
{ 
    // Get the Location instance intended to be the center of the radius by using the key
    // Do a radius search around it using (int)parameters["radius"] as the radius
    // return the IQueryable<Location> of all location found within that radius
}

ODataModelBuilder modelBuilder = new ODataConventionModelBuilder();
modelBuilder.EntitySet<Location>("Locations");

// New Code
ActionConfiguration getLocations = modelBuilder.Entity<Location>().Action("GetLocationsWithinRadius");
getLocations.Parameter<int>("radius");
getLocations.Returns<IQueryable<Location>>();

I would love to get this to work and currently it doesn't work when the the return type is an IQueryable<Location>. If the return type is a primitive like an int, then it works, otherwise it gives the following error when I create a post in fiddler (the post is something like http://localhost:2663/odata/Locations(2112)/GetLocationsWithinRadius and the Request Body is {radius: 50}):

{
  "odata.error":{
    "code":"","message":{
      "lang":"en-US","value":"An error has occurred."
    },"innererror":{
      "message":"The 'ObjectContent`1' type failed to serialize the response body for content type 'application/json; odata=minimalmetadata; streaming=true; charset=utf-8'.","type":"System.InvalidOperationException","stacktrace":"","internalexception":{
        "message":"The related entity set could not be found from the OData path. The related entity set is required to serialize the payload.","type":"System.Runtime.Serialization.SerializationException","stacktrace":"   at System.Web.Http.OData.Formatter.Serialization.ODataFeedSerializer.WriteObject(Object graph, ODataMessageWriter messageWriter, ODataSerializerContext writeContext)\r\n   at System.Web.Http.OData.Formatter.ODataMediaTypeFormatter.<>c__DisplayClassa.<WriteToStreamAsync>b__9()\r\n   at System.Threading.Tasks.TaskHelpers.RunSynchronously(Action action, CancellationToken token)"
      }
    }
  }
}

Is it possible to do what I am trying to accomplish? And if it is, dare I ask if the returned IQueryable<Location> becomes composable with odata paramaters...(that would be nice)?

Thanks

Answer 1

Looks like your action configuration is incorrect. Try the following and see if it works:

//getLocations.Returns<IQueryable<Location>>();
getLocations.ReturnsCollectionFromEntitySet<Location>("Locations");