Handle multiple endpoints in .NET Core 3.1 Web API by Query Params

Question

I am migrating controllers from .NET Framework to .NET Core and I want to be compatibility with API calls from previous version. I have problem with handling multiple routes from Query Params.

My example controller:

[Route("/api/[controller]")]
[Route("/api/[controller]/[action]")]
public class StaticFileController : ControllerBase
{
    [HttpGet("{name}")]
    public HttpResponseMessage GetByName(string name)
    {
    }

    [HttpGet]
    public IActionResult Get()
    {
    }
}

Calling api/StaticFile?name=someFunnyName will lead me to Get() action instead of expected GetByName(string name).

What I want to achieve:

• Calling GET api/StaticFile -> goes to Get() action
• Calling GET api/StaticFile?name=someFunnyName -> goes to GetByName() action

My app.UseEndpoints() from Startup.cs have only these lines:

endpoints.MapControllers();
endpoints.MapDefaultControllerRoute();

If I use [HttpGet] everywhere and add ([FromQuery] string name) it gets me AmbiguousMatchException: The request matched multiple endpoints

Thank you for your time to helping me (and maybe others)

Answer 1

What I want to achieve:

• Calling GET api/StaticFile -> goes to Get() action
• Calling GET api/StaticFile?name=someFunnyName -> goes to GetByName() action

To achieve above requirement of matching request(s) to expected action(s) based on the query string, you can try to implement a custom ActionMethodSelectorAttribute and apply it to your actions, like below.

[AttributeUsage(AttributeTargets.Method, AllowMultiple = true)]
public class QueryStringConstraintAttribute : ActionMethodSelectorAttribute
{
    public string QueryStingName { get; set; }
    public bool CanPass { get; set; }
    public QueryStringConstraintAttribute(string qname, bool canpass)
    {
        QueryStingName = qname;
        CanPass = canpass;
    }
    public override bool IsValidForRequest(RouteContext routeContext, ActionDescriptor action)
    {
        StringValues value;

        routeContext.HttpContext.Request.Query.TryGetValue(QueryStingName, out value);

        if (QueryStingName == "" && CanPass)
        {
            return true;
        }
        else
        {
            if (CanPass)
            {
                return !StringValues.IsNullOrEmpty(value);
            }

            return StringValues.IsNullOrEmpty(value);
        }
    }
}

Apply to Actions

[Route("api/[controller]")]
[ApiController]
public class StaticFileController : ControllerBase
{
    [HttpGet]
    [QueryStringConstraint("name", true)]
    [QueryStringConstraint("", false)]
    public IActionResult GetByName(string name)
    {
        return Ok("From `GetByName` Action");
    }

    [HttpGet]
    [QueryStringConstraint("name", false)]
    [QueryStringConstraint("", true)]
    public IActionResult Get()
    {
        return Ok("From `Get` Action");
    }
}

Test Result