c# - Dependency injection not working with Owin self-hosted Web Api 2 and Autofac

Question

I'm finding my feet with Web Api 2, Owin and Autofac and need some guidance, please.

Overview
I have an Owin self-hosted Web Api that uses Autofac for IoC and dependency injection. The project is a console app acting like a service, meaning it can be stopped and started. I have an Authentication controller with two constructors: one parameter-less and the other injects a repository.

Problem
When I run the service and call the api, my parameter-less constructor is called and my repository never gets injected (_repository = null).

Research
I've done a fair bit of research and found some helpful projects on Github, which I replicated to the tee but I'm missing a big part of the puzzle. This was helpful but didn't solve my problem. I read this question on Stack Overflow and Dane Sparza had a nice demo project but I couldn't find a clear solution. The problem is not the self-hosting but the dependency injection.

My code (thinned out for explanation)

public class Startup
{
    public void Configuration(IAppBuilder app)
    {
        HttpConfiguration config = new HttpConfiguration();

        config.Routes.MapHttpRoute(
            name: "DefaultApi",
            routeTemplate: "api/{controller}/{id}",
            defaults: new { id = RouteParameter.Optional }
        );

        var json = config.Formatters.JsonFormatter;
        json.SerializerSettings.PreserveReferencesHandling = Newtonsoft.Json.PreserveReferencesHandling.Objects;
        config.Formatters.Remove(config.Formatters.XmlFormatter);

        var connectioninfo = ConnectionInfo.FromAppConfig("mongodb");

        var builder = new ContainerBuilder();                                    // Create the container builder.
        builder.RegisterApiControllers(Assembly.GetExecutingAssembly());         // Register the Web API controllers.
        builder.Register(c => new Logger()).As<ILogger>().InstancePerRequest();  // Register a logger service to be used by the controller and middleware.
        builder.RegisterType<AuthenticationRepository>().As<IAuthenticationRepository>().WithParameter(new NamedParameter("connectionInfo", connectioninfo)).InstancePerRequest();

        var container = builder.Build();

        var resolver = new AutofacWebApiDependencyResolver(container);           // Create an assign a dependency resolver for Web API to use.
        GlobalConfiguration.Configuration.DependencyResolver = resolver;         // Configure Web API with the dependency resolver

        app.UseCors(CorsOptions.AllowAll);  
        app.UseWebApi(config);
        app.UseAutofacWebApi(config);  // Make sure the Autofac lifetime scope is passed to Web API.
    }

Program.cs

 static void Main(string[] args)
    {           
        var service = new ApiService(typeof(Program), args);

        var baseAddress = "http://localhost:9000/";
        IDisposable _server = null;

        service.Run(
           delegate()
           {
               _server = WebApp.Start<Startup>(url: baseAddress);
           },
           delegate()
           {
               if (_server != null)
               {
                   _server.Dispose();
               }
           }
       );
    }

ApiController

public class AuthenticationController : ApiController
{
    private IAuthenticationRepository _repository;

    public AuthenticationController() { }

    public AuthenticationController(IAuthenticationRepository repository)
    {
        _repository = repository;
    }

    [AllowAnonymous]
    public IHttpActionResult Authenticate(string name, string password)
    {
        if (_repository == null)
            return BadRequest("User repository is null.");

        var valid = _repository.AuthenticateUser(name, password);
        return Ok(valid);
    }
}

Answer 1

You should be using the HttpConfiguration with which you're bootstrapping OWIN everywhere. So, this:

GlobalConfiguration.Configuration.DependencyResolver = resolver;

Should become:

config.DependencyResolver = resolver;

Other than that, everything looks good. Api controllers are registered, although you're not giving them a scope. Not sure if in Autofac scoping defaults to per-request for controllers or if it has the notion of per-request scoping at all (I know that LightInject has it).

Looking around, I think you followed the example on the Google Code repo for Autofac, which indeed uses GlobalConfiguration. Instead, if you look at the GitHub example, it is a bit different. Try to make the changes according to this. Including this:

// This should be the first middleware added to the IAppBuilder.
app.UseAutofacMiddleware(container);

---

2016 update

What I said above still applies, but something extra from Autofac's docs (thanks Brad):

A common error in OWIN integration is use of the GlobalConfiguration.Configuration. In OWIN you create the configuration from scratch. You should not reference GlobalConfiguration.Configuration anywhere when using the OWIN integration.