Attribute routing and MapGroup()

[MichalSznajder]

Let's consider following program:

var builder = WebApplication.CreateBuilder(args);

builder.Services.AddControllersWithViews();

var app = builder.Build();

app.UseRouting();
app.MapGroup("Group")
    .MapControllerRoute(name: "default",
        pattern: "Home/Conventional",
        defaults: new { controller = "Home", action = "Conventional" });

app.Run();

public class HomeController : Controller
{
    public IActionResult Conventional()
    {
        return Content("Conventional");
    }

    [Route("/Home/Attribute")]
    public IActionResult Attribute()
    {
        return Content("Attribute");
    }
}

I have one controller that mixes both conventional (albeit "fixed") and attribute routing.

Could someone give me hints why following works:

$ curl -i http://localhost:5090/Group/Home/Attribute
HTTP/1.1 200 OK
Content-Length: 9
Content-Type: text/plain; charset=utf-8
Date: Sat, 13 Sep 2025 08:48:30 GMT
Server: Kestrel

Attribute%

Suddenly attribute route is attached to a group. Is there a way to prevent it?

Background: I want to create conventional routing similar to Rails resources and group them with MapGroup(). However still I have still some attribute routed controllers and they got attached to various groups.

[engineering87]

Hello @MichalSznajder,
this is the expected behavior. MapControllerRoute() maps both conventional and attribute routing controller actions.
When you call it on a route group, the group’s prefix is applied to all endpoints it adds /Group/Home/Attribute works.
To prevent it, you have to map attribute routes outside the group and only put conventional routes in the group:

app.UseRouting();

app.MapControllers(); // attribute-routed controllers (no group)

app.MapGroup("/Group")
   .MapControllerRoute("fixed", "Home/Conventional",
       new { controller = "Home", action = "Conventional" });

This keeps attribute-routed actions from inheriting the group prefix

[MichalSznajder]

I tried this solution and attribute controllers are mapped both in group and "at root":

$ curl -i http://localhost:5090/Home/Attribute
HTTP/1.1 200 OK
Content-Length: 9
Content-Type: text/plain; charset=utf-8
Date: Sun, 14 Sep 2025 08:54:55 GMT
Server: Kestrel

Attribute%
$ curl -i http://localhost:5090/Group/Home/Attribute
HTTP/1.1 200 OK
Content-Length: 9
Content-Type: text/plain; charset=utf-8
Date: Sun, 14 Sep 2025 08:54:57 GMT
Server: Kestrel

Attribute%

This solution was suggested by AI and I think also found it on some websites.

I wonder if this is a bug in net8 or general issue.

[MichalSznajder]

I just tried on 10.0.100-rc.1.25451.107 but it is the same. On osx but it should not matter.