Select ASP.NET Web API Controller depending on route value (namespace)

Question

I am trying to add various Web API plugins to my MVC website. Copying and pasting DLLs of API files allow me to call appropriate service methods using the default route - hostname/api/{controller}/{id}, but it throws an error, when I have controllers with the same name but in different locations (DLLs, namespaces). The error message is something like this (which is normal):

Multiple types were found that match the controller named 'Names'. This can happen if the route that services this request ('api/{controller}/{id}') found multiple controllers defined with the same name but differing namespaces, which is not supported. The request for 'Names' has found the following matching controllers: ApiExt.NamesController ApiExt1.NamesController

I have the same "Names" controller in different DLLs (namespaces) ApiExt, ApiExt1.

I already found a similar topic to select controller depending of API version - http://shazwazza.com/post/multiple-webapi-controllers-with-the-same-name-but-different-namespaces/ , but this is not quite what I need. I need to select the controller (namespace) depending on route value, something like this:

hostname/api/{namespace}/{controller}/{id}

I believe this is absolutely possible, but I'm not familiar with overriding MVC controller selector (implementing IHttpControllerSelector).

Any suggestions?

Thank you.

Answer 1

You can definitely achieve this. You need to write your own Controller Selector by implementing IHttpControllerSelector . Please refer to this link for detailed, step-by-step explanation.

Answer 2

The blog post describing a solution, https://blogs.msdn.microsoft.com/webdev/2013/03/07/asp-net-web-api-using-namespaces-to-version-web-apis/ , doesnt contain the complete code and has a bad link to what used to provide it.

Here's a blob providing the class, original from Umbraco

https://github.com/WebApiContrib/WebAPIContrib/blob/master/src/WebApiContrib/Selectors/NamespaceHttpControllerSelector.cs ,

Full listing in case it's removed:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Net.Http;
using System.Web.Http;
using System.Web.Http.Controllers;
using System.Web.Http.Dispatcher;

namespace WebApiContrib.Selectors
{
    //originally created for Umbraco https://github.com/umbraco/Umbraco-CMS/blob/7.2.0/src/Umbraco.Web/WebApi/NamespaceHttpControllerSelector.cs
    //adapted from there, does not recreate HttpControllerDescriptors, instead caches them
    public class NamespaceHttpControllerSelector : DefaultHttpControllerSelector
    {
        private const string ControllerKey = "controller";
        private readonly HttpConfiguration _configuration;
        private readonly Lazy<HashSet<NamespacedHttpControllerMetadata>> _duplicateControllerTypes;

        public NamespaceHttpControllerSelector(HttpConfiguration configuration)
            : base(configuration)
        {
            _configuration = configuration;
            _duplicateControllerTypes = new Lazy<HashSet<NamespacedHttpControllerMetadata>>(InitializeNamespacedHttpControllerMetadata);
        }

        public override HttpControllerDescriptor SelectController(HttpRequestMessage request)
        {
            var routeData = request.GetRouteData();
            if (routeData == null || routeData.Route == null || routeData.Route.DataTokens["Namespaces"] == null)
                return base.SelectController(request);

            // Look up controller in route data
            object controllerName;
            routeData.Values.TryGetValue(ControllerKey, out controllerName);
            var controllerNameAsString = controllerName as string;
            if (controllerNameAsString == null)
                return base.SelectController(request);

            //get the currently cached default controllers - this will not contain duplicate controllers found so if
            // this controller is found in the underlying cache we don't need to do anything
            var map = base.GetControllerMapping();
            if (map.ContainsKey(controllerNameAsString))
                return base.SelectController(request);

            //the cache does not contain this controller because it's most likely a duplicate, 
            // so we need to sort this out ourselves and we can only do that if the namespace token
            // is formatted correctly.
            var namespaces = routeData.Route.DataTokens["Namespaces"] as IEnumerable<string>;
            if (namespaces == null)
                return base.SelectController(request);

            //see if this is in our cache
            var found = _duplicateControllerTypes.Value.FirstOrDefault(x => string.Equals(x.ControllerName, controllerNameAsString, StringComparison.OrdinalIgnoreCase) && namespaces.Contains(x.ControllerNamespace));
            if (found == null)
                return base.SelectController(request);

            return found.Descriptor;
        }

        private HashSet<NamespacedHttpControllerMetadata> InitializeNamespacedHttpControllerMetadata()
        {
            var assembliesResolver = _configuration.Services.GetAssembliesResolver();
            var controllersResolver = _configuration.Services.GetHttpControllerTypeResolver();
            var controllerTypes = controllersResolver.GetControllerTypes(assembliesResolver);

            var groupedByName = controllerTypes.GroupBy(
                t => t.Name.Substring(0, t.Name.Length - ControllerSuffix.Length),
                StringComparer.OrdinalIgnoreCase).Where(x => x.Count() > 1);

            var duplicateControllers = groupedByName.ToDictionary(
                g => g.Key,
                g => g.ToLookup(t => t.Namespace ?? String.Empty, StringComparer.OrdinalIgnoreCase),
                StringComparer.OrdinalIgnoreCase);

            var result = new HashSet<NamespacedHttpControllerMetadata>();

            foreach (var controllerTypeGroup in duplicateControllers)
            {
                foreach (var controllerType in controllerTypeGroup.Value.SelectMany(controllerTypesGrouping => controllerTypesGrouping))
                {
                    result.Add(new NamespacedHttpControllerMetadata(controllerTypeGroup.Key, controllerType.Namespace,
                        new HttpControllerDescriptor(_configuration, controllerTypeGroup.Key, controllerType)));
                }
            }

            return result;
        }

        private class NamespacedHttpControllerMetadata
        {
            private readonly string _controllerName;
            private readonly string _controllerNamespace;
            private readonly HttpControllerDescriptor _descriptor;

            public NamespacedHttpControllerMetadata(string controllerName, string controllerNamespace, HttpControllerDescriptor descriptor)
            {
                _controllerName = controllerName;
                _controllerNamespace = controllerNamespace;
                _descriptor = descriptor;
            }

            public string ControllerName
            {
                get { return _controllerName; }
            }

            public string ControllerNamespace
            {
                get { return _controllerNamespace; }
            }

            public HttpControllerDescriptor Descriptor
            {
                get { return _descriptor; }
            }
        }
    }
}

Then just add the Namespaces token to the route

route.DataTokens["Namespaces"] = new string[] {"Foo.Controllers"};

It's also more production ready with the caching.