asp-action tag helper doesn't work with Route attribute on controller - .net-core-3.1

Question

I tried to do some simple thing. I wanted to have different action name and different method name:
public class SuperController: Controller
{
[HttpGet("dosth")]
public IActionResult DoSomethingWithThoseParameters(int id, string token)
{
}
}
Look that there is no Route attribute on the controller.
In such case tag helper asp-action works perfectly. But I thought that my action dosth would be placed in: localhost/Super/dosth
But it was not. So I figured it out that I probably should set the route for the whole controller, like this:
[Route("[controller]")]
public class SuperController: Controller
{
[HttpGet("dosth")]
public IActionResult DoSomethingWithThoseParameters(int id, string token)
{
}
public IActionResult Register()
{
return View();
}
}
But now asp-action stopped working. For example:
<a asp-controller="Super" asp-action="Register">
creates anchor to: localhost/Super and not to: localhost/Super/Register
When I remove Route tag from controller it works again.
My mappings are configured as standard says:
app.UseEndpoints(endpoints =>
{
endpoints.MapControllerRoute(
name: "default",
pattern: "{controller=Home}/{action=Index}/{id?}");
endpoints.MapRazorPages();
});
So, how come asp-action does not work when there is a Route attribute on the whole controller

Answer 1

Applying [Route] attribute on a controller enables attribute routing for all controller methods. So, by doing so you force yourself to provide the route for every method (in one way or another).
With [Route("[controller]")] the base route template for your controller actions is just the controller name, so if you have multiple actions without [Route] or [HttpGet] (and other HTTP verbs) attributes applied on them:
[Route("[controller]")]
public class SuperController: Controller
{
public IActionResult DoSomethingWithThoseParameters(int id, string token)
{
}
public IActionResult Register()
{
return View();
}
}
...you get yourself a AmbiguousMatchException because multiple controller actions will be matching same route:
/Super
You can either explicitly specify the route for every action:
[Route("[controller]")]
public class SuperController: Controller
{
[HttpGet("dosth")]
public IActionResult DoSomethingWithThoseParameters(int id, string token)
{
}
[HttpGet("Register")]
public IActionResult Register()
{
return View();
}
}
or specify action name as an part of expected route already on controller level:
[Route("[controller]/[action]")]
public class SuperController : Controller
{
public IActionResult DoSomethingWithThoseParameters(int id, string token)
{
}
public IActionResult Register()
{
return View();
}
}
then, you don't have to specify the routes for actions, because you applied a route template on a controller level. Your actions will inherit that route template.
But, be aware that in order to overwrite it you'll have to overwrite it all, otherwise you'll append to the route template.
[HttpGet("/[controller]/dosth")]
public IActionResult DoSomethingWithThoseParameters(int id, string token)
{
}
Read more about routing in official documentation.