MVC 属性路由 RoutePrefix 不适用于默认路由

Question

I have a work-around, but I'd really like to know why this doesn't appear to work in MVC. (.Net 4.6.1)

I have a controller which I want to use a RoutePrefix:

[RoutePrefix("entry")]
public class DefaultController : Controller
{
    [HttpGet]
    [Route(), Route("Index")]
    public ActionResult Index()
    {
        // ...
    }
}

In the route config:

routes.IgnoreRoute("{resource}.axd/{*pathInfo}");

routes.MapMvcAttributeRoutes();

routes.MapRoute(
    name: "Default",
    url: "{controller}/{action}/{id}",
    defaults: new { controller = "entry", action = "index", id = UrlParameter.Optional }

The issue is that with this configuration, running under local IIS to test, navigating to "localhost/testApp/entry" works, "localhost/testApp/entry/index" works, however the default "localhost/testApp/" results in a 404.

This has been doing my head in because on a fresh project with the default controllers and a default set to "home" and "index" the "localhost/testApp" would render Home/Index without an issue.

I narrowed it down to the RoutePrefix being the issue. If I remove the RoutePrefix and change the defaults to: new { controller = "default", action = "index", id = UrlParameter.Optional }

Then "localhost/testApp" works, but obviously this requires using /default for other routes rather than /entry.

Also, if I leave the prefix in (switching the default controller back to "entry") and add Route("~/") to the Index method, then "localhost/testApp" also works as according to the doco that a ~ route overrides the route prefix.

I'd like to know if there is an explanation why RoutePrefix doesn't seem to play nice with default routing? I'm fine with adding a ~/ route for that default action, but it seems I'm missing some understanding on how RoutePrefix is intended to be used.

Answer 1

Action attribute routing has the highest priority. If you use it only route attributes will be working, everything else will be ignored. You can to one action as many routes as you need.

Since you have 2 variants - Route() and Route("Index") it works only for 2 urls -"localhost/testApp/entry" and "localhost/testApp/entry/index".

if you remove Route() it will work only for one url-lcalhost/testApp/entry/index".

If you add 3rd Route("~/") it will work for 3rd url "localhost/testApp" Sign ~ means that any prefixes should be ignored, it starts from root.

So you can not use default conventional routing on Index action since it is only obeys routing attributes.

Also, you have a controller [RoutePrefix("entry")] attribute routing too and it that next highest priority and because of this it overrides your convention routing in the config file. This is why default routing doesn't work for this controller and it doesn't go to Index automaticaly. To make default route work you need to remove route prefix and fix web config

defaults: new { controller = "default", action = "index", id = UrlParameter.Optional }

Current default controller = "entry" doesn't exist at all.

So you have two choices to have Index as default route action - remove all attribute routing and lost all another extra routes or add one more.

Answer 2

Thanks to Serge for helping point out a bad assumption I had about [RoutePrefix] . The problem here turns out that [RoutePrefix] is not a substitute name for a controller, (though that is how it behaves on the surface) but rather a prefix to each individual action. While the mapping in the URL will be identical:

Example 1:

public class EntryController
{
    public ActionResult Index() { ... }
}

Example 2:

[RoutePrefix("Entry")]
public class DefaultController
{
    [Route("Index")]
    public ActionResult Index() { ... }
}

Both of these examples would resolve "localhost/testApp/entry/index", however only the first mapping would be considered as a match for {controller}/{action} and resolve a "defaults" mapping of "entry/index".

So if an action /w Attribute-based routing needs to be made a root default you need to explicitly declare it as the root using [Route()] if there is no [RoutePrefix] , or [Route("~/")] if there is a [RoutePrefix] . since it won't be included in the {controller}/{action} routing. (Verified by removing the Default {controller}/{action} routing entirely).