Web API 2 RoutePrefix does not working

Question

When defining a RoutePrefix at controller level, when I try to access the API class using the URL with prefix http://localhost:55020/api/v2/dummy/get it throws 404. This http://localhost:55020/api/dummy/get works absolutely fine though.

Here is controller class which has a RoutePrefix defined

    [RoutePrefix("v2/dummy")]
    public class DummyController : ApiController
    {
        // GET api/values
        [SwaggerOperation("Get")]
        public IEnumerable<string> Get()
        {
            return new string[] { "value1", "value2", "value3" };
        }
    }

Here is WebApiConfig

 public static class WebApiConfig
    {
        public static void Register(HttpConfiguration config)
        {
            // Web API configuration and services

            // Web API routes
            config.MapHttpAttributeRoutes();

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

Answer 1

Use attribute routing instead

public class DummyController : ApiController
{
    // GET api/values
    [HttpGet]
    [Route("api/v2/dummy/get")]
    public IEnumerable<string> Get()
    {
        return new string[] { "value1", "value2", "value3" };
    }
}

and if you want route prefix then

[RoutePrefix("api/v2/dummy")]
public class DummyController : ApiController
{
    // GET api/v2/dummy
    [HttpGet]
    [Route("get")]
    public IEnumerable<string> Get()
    {
        return new string[] { "value1", "value2", "value3" };
    }
}

Answer 2

You are mixing up how attribute routing and convention-based routing work.

This is full attribute routing.

[RoutePrefix("api/v2/dummy")]
public class DummyController : ApiController
{
    // GET api/v2/dummy/get
    [HttpGet]
    [Route("get")]
    [SwaggerOperation("Get")]
    public IEnumerable<string> Get()
    {
        return new string[] { "value1", "value2", "value3" };
    }
}

If you want to do the same thing via convention-based routing

public static class WebApiConfig
{
    public static void Register(HttpConfiguration config)
    {
        // Web API configuration and services

        // Web API routes
        config.MapHttpAttributeRoutes();

        config.Routes.MapHttpRoute(
            name: "DummyApi",
            routeTemplate: "api/v2/dummy/{action}",
            defaults: new { controller = "Dummy" }
        );

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