Attribute routes missing from routing table when using multiple namespaces

Question

I am using namespace versioning in my web api (4.0) project. I'm using Attribute routing to define custom routes for our actions. This works just fine when a controller only exists in one namespace/version.

But when a controller exists in both namespaces/versions, the attribute route is ignored completely. I am using the solution here to look at what routes are in the routing table. And it only contains one route, for my "single" controller. If I delete/comment out/change the name of the controller in V2, then suddenly the "double" controller's route appears in the routing table as well.

Is there any reason that an attribute route would be ignored because the same class/controller name exists in 2 different namespaces? Here is my code, broken down to the simplest failing example:

namespace API.v1
{
    public class SingleController : ApiController
    {
        [HttpGet]
        [Route("api/{version}/Single")]
        public string Test()
        {
            return "Response";
        }
    }
}

This class/route works just fine. http://localhost:57560/api/v1/Single returns "Response".

namespace API.v1
{
    public class DoubleController : ApiController
    {
        [HttpGet]
        [Route("api/{version}/Double")]
        public string Test()
        {
            return "Response";
        }
    }
}

namespace API.v2
{
    public class DoubleController : ApiController
    {
        [HttpGet]
        [Route("api/{version}/Double")]
        public string Test()
        {
            return "Response";
        }
    }
}

These 2 classes fail; the attribute route is missing from the routing table, and http://localhost:57560/api/v1/Double returns 404, as well as http://localhost:57560/api/v2/Double. If I just change the name of the v2.Double class, then it works just fine.

In this example, I have no default routes set up at all; only the Attribute routing. When using default routes, the versioning and routing work just fine:

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

This route works perfectly across multiple versions. But I need it to work with attribute routing.

Did you try using RoutePrefix in your controller with your namespace? [RoutePrefix("api/v2")]. We use this way to keep multiple versions of our controllers. — jpgrassi
How are you populating the version in your routing? Somewhere you should have a constraint to handle that. I think that @jpgrassi 's idea to use a route prefix on the controller is really your best bet. — MichaelDotKnox
Using RoutePrefix in your controller also prevents you from repeating the [Route("api/{version}/Double")] in each action. — jpgrassi
@jpgrassi - RoutePrefix makes no difference at all. I was using a custom HttpControllerSelector to find the correct controller class based on the {version} in the route, but none of that code even gets hit in this case. I tried replacing {version} in each controller with specific v1 and v2 (which allowed me to remove the custom ControllerSelector), but it makes no difference. — GendoIkari
The sample always matches the value of “namespace” against the final segment of the namespace (i.e., the inner scope). So “v1” matches “MyApp.Controllers.V1” but not “MyApp.V1.Controllers”. You could change this behavior by modifying the code that constructs the dictionary of controller types. (See the InitializeControllerDictionary method.) — Ahmed Abdelraouf

GendoIkari GendoIkari · Accepted Answer · 2016-01-05T17:01:54

I have been able to solve the issue using the solution here: http://abhinawblog.blogspot.com/2014/12/web-api-versioning-using.html. The problem appears to be related to the way that attribute routing differs from using the default routes table. It is required that the routes have unique names, and that the version numbers in the routes have custom constraints put on them.

Attribute routes missing from routing table when using multiple namespaces

2 Answers