DeeperNavigationsRoutingConvention.cs

public class DeeperNavigationsRoutingConvention : EntitySetRoutingConvention
{
    public override string SelectAction(ODataPath odataPath, HttpControllerContext controllerContext, ILookup<string, HttpActionDescriptor> actionMap)
    {
        if (odataPath.PathTemplate == "~/entityset/key/navigation/key") // ~/Customers(10)/Orders(42)
        {
            IEdmNavigationProperty navigationProperty = (odataPath.Segments[2] as NavigationPathSegment).NavigationProperty;
            IEdmEntityType navigationPropertyType = navigationProperty.Type.AsCollection().ElementType().AsEntity().EntityDefinition(); // collection of entity.
            controllerContext.RouteData.Values["key1"] = (odataPath.Segments[1] as KeyValuePathSegment).Value;
            controllerContext.RouteData.Values["key2"] = (odataPath.Segments[3] as KeyValuePathSegment).Value;
            return "Get" + navigationPropertyType.Name;  // Maps to controller action Order GetOrder([FromODataUri]int key1, [FromODataUri]int key2)
        }

        return null;
    }
}

class Program
{
    static void Main(string[] args)
    {
        // Add the custom routing convention to the default routing conventions.
        IList<IODataRoutingConvention> routingConventions = ODataRoutingConventions.CreateDefault();
        routingConventions.Insert(0, new DeeperNavigationsRoutingConvention());

        var builder = new ODataConventionModelBuilder();
        builder.EntitySet<Customer>("Customers");
        builder.EntitySet<Order>("Orders");

        HttpConfiguration config = new HttpConfiguration();
        
        // map odata route with the custom routing convention included.
        config.Routes.MapODataRoute("OData", "odata", builder.GetEdmModel(), new DefaultODataPathHandler(), routingConventions);
    }
}