OData v4 Custom Function

Question

I'm trying to create a custom function in an OData v4 Web API solution. I need to return a collection of "Orders" based on unique logic that can't be handled natively by OData. I cannot seem to figure out how to create this custom function without destroying the entire OData service layer. When I decorate the Controller method with an ODataRoute attribute it all goes to hell. Any basic request produces the same error. Can someone please take a look at the code below and see if you notice something that I must be missing?

WebApiConfig.cs

public static class WebApiConfig
{
    public static void Register(HttpConfiguration config)
    {

        config.MapHttpAttributeRoutes();

        config.Routes.MapHttpRoute(
            name: "DefaultApi",
            routeTemplate: "api/{controller}/{id}",
            defaults: new { id = RouteParameter.Optional }
        );

        config.MapODataServiceRoute("odata", "odata", model: GetModel());
    }

    public static Microsoft.OData.Edm.IEdmModel GetModel()
    {
        ODataModelBuilder builder = new ODataConventionModelBuilder();
        builder.EntitySet<Account>("Accounts");
        builder.EntitySet<Email>("Emails");
        builder.EntitySet<PhoneNumber>("PhoneNumbers");
        builder.EntitySet<Account>("Accounts");
        builder.EntitySet<Address>("Addresses");
        builder.EntitySet<Order>("Orders");
        builder.EntitySet<OrderDetail>("OrderDetails");

        var orders = builder.EntityType<Order>();
        var function = orders.Function("GetByExternalKey");
        function.Parameter<long>("key");
        function.ReturnsCollectionFromEntitySet<Order>("Orders");

        return builder.GetEdmModel();
     }
 }

OrdersController.cs

public class OrdersController : ODataController
{
    private SomeContext db = new SomeContext();

    ...Other Stuff...

    [HttpGet]
    [ODataRoute("GetByExternalKey(key={key})")]
    public IHttpActionResult GetByExternalKey(long key)
    {
       return Ok(from o in db.Orders
          where //SpecialCrazyStuff is done
          select o);
    }
}
}

When issuing ANY request against the OData layer I receive the following error response.

The path template 'GetByExternalKey(key={key})' on the action 'GetByExternalKey' in controller 'Orders' is not a valid OData path template. Resource not found for the segment 'GetByExternalKey'.

Solution

Per the model builder, the function GetByExternalKey is a bound function. According to the OData Protocol v4, a bound function is invoked through the namespace or alias qualified named, so you need to add more in the route attribute:

[HttpGet]
[ODataRoute("Orders({id})/Your.Namespace.GetByExternalKey(key={key})")]
public IHttpActionResult GetByExternalKey(long key)
{
   return Ok(from o in db.Orders
      where//SpecialCrazyStuff is done
      select o);
}

If you don't know the namespace, just add below to the method GetModel():

builder.Namespace = typeof(Order).Namespace;

And replace "Your.Namespace" with the namespace of the type Order.

Here are 2 samples related to your question, just for your reference: https://aspnet.codeplex.com/SourceControl/latest#Samples/WebApi/OData/v4/ODataFunctionSample/

https://aspnet.codeplex.com/SourceControl/latest#Samples/WebApi/OData/v4/ODataAttributeRoutingSample/