How to retrieve RouteValues in ActionSelector in ASP.NET Core - asp.net-core

Question

I've created a GitHub repo to better understand the problem here. I have two actions on two different controllers bound to the same route.
http://localhost/sameControllerRoute/{identifier}/values
[Route("sameControllerRoute")]
public class FirstController : Controller
{
public FirstController()
{
// different EF Core DataContext than SecondController and possibly other dependencies than SecondController
}
[HttpGet("{identifier}/values")]
public IActionResult Values(string identifier, DateTime from, DateTime to) // other parameters than SecondController/Values
{
return this.Ok("Was in FirstController");
}
}
[Route("sameControllerRoute")]
public class SecondController : Controller
{
public SecondController()
{
// different EF Core DataContext than FirstController and possibly other dependencies than FirstController
}
[HttpGet("{identifier}/values")]
public IActionResult Values(string identifier, int number, string somethingElse) // other parameters than FirstController/Values
{
return this.Ok("Was in SecondController");
}
}
Since there are two matching routes, the default ActionSelector fails with:
'[...] AmbiguousActionException: Multiple actions matched. [...]'
which is comprehensible.
So I thought I can implement my own ActionSelector. In there I would implement the logic that resolves the issue of multiple routes via same logic depending on the 'identifier' route value (line 27 in code)
If 'identifier' value is a --> then FirstController
If 'identifier' value is b --> then SecondController
and so on...
protected override IReadOnlyList<ActionDescriptor> SelectBestActions(IReadOnlyList<ActionDescriptor> actions)
{
if (actions.HasLessThan(2)) return base.SelectBestActions(actions); // works like base implementation
foreach (var action in actions)
{
if (action.Parameters.Any(p => p.Name == "identifier"))
{
/*** get value of identifier from route (launchSettings this would result in 'someIdentifier') ***/
// call logic that decides whether value of identifier matches the controller
// if yes
return new List<ActionDescriptor>(new[] { action }).AsReadOnly();
// else
// keep going
}
}
return base.SelectBestActions(actions); // fail in all other cases with AmbiguousActionException
}
But I haven't found a good solution to get access to the route values in ActionSelector. Which is comprehensible as well because ModelBinding hasn't kicked in yet since MVC is still trying to figure out the Route.
A dirty solution could be to get hold of IHttpContextAccessor and regex somehow against the path.
But I'm still hoping you could provide a better idea to retrieve the route values even though ModelBinding hasn't happend yet in the request pipeline.

Answer 1

Not sure that you need to use ActionSelector at all for your scenario. Accordingly, to provided code, your controllers works with different types of resources (and so they expect different query parameters). As so, it is better to use different routing templates. Something like this for example:
FirstController: /sameControllerRoute/resourceA/{identifier}/values
SecondController: /sameControllerRoute/resourceB/{identifier}/values
In the scope of REST, when we are talking about /sameControllerRoute/{identifier}/values route template, we expect that different identifier means the same resource type, but different resource name. And so, as API consumers, we expect that all of the following requests are supported
/sameControllerRoute/a/values?from=20160101&to=20170202
/sameControllerRoute/b/values?from=20160101&to=20170202
/sameControllerRoute/a/values?number=1&somethingElse=someData
/sameControllerRoute/b/values?number=1&somethingElse=someData
That is not true in your case

Answer 2

I ended up implementing the proposed solution by the ASP.NET team. This was to implement an IActionConstrain as shown here:
// Copyright (c) .NET Foundation. All rights reserved.
// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
using System;
using Microsoft.AspNetCore.Mvc.ActionConstraints;
namespace ActionConstraintSample.Web
{
public class CountrySpecificAttribute : Attribute, IActionConstraint
{
private readonly string _countryCode;
public CountrySpecificAttribute(string countryCode)
{
_countryCode = countryCode;
}
public int Order
{
get
{
return 0;
}
}
public bool Accept(ActionConstraintContext context)
{
return string.Equals(
context.RouteContext.RouteData.Values["country"].ToString(),
_countryCode,
StringComparison.OrdinalIgnoreCase);
}
}
}
https://github.com/aspnet/Entropy/blob/dev/samples/Mvc.ActionConstraintSample.Web/CountrySpecificAttribute.cs