Autofac allows multiple instances of the same type.

Question

I have a slightly modified version of Mediatr that handles command processing in my application. I implemented MediatorPipeline, which allows me to have before and after processors.

public class AsyncMediatorPipeline<TRequest, TResponse> 
    : IAsyncRequestHandler<TRequest, TResponse> 
    where TRequest : IAsyncRequest<TResponse>
{
    private readonly IAsyncRequestHandler<TRequest, TResponse> inner;
    private readonly IAsyncPreRequestHandler<TRequest>[] preRequestHandlers;
    private readonly IAsyncPostRequestHandler<TRequest,TResponse>[] postRequestHandlers;

    public AsyncMediatorPipeline(IAsyncRequestHandler<TRequest, TResponse> inner, 
        IAsyncPreRequestHandler<TRequest>[] preRequestHandlers, 
        IAsyncPostRequestHandler<TRequest, TResponse>[] postRequestHandlers)
    {
        this.inner = inner;
        this.preRequestHandlers = preRequestHandlers;
        this.postRequestHandlers = postRequestHandlers;
    }

    public async Task<TResponse> Handle(TRequest message)
    {
        foreach (var preRequestHandler in preRequestHandlers)
        {
            await preRequestHandler.Handle(message);
        }

        var result = await inner.Handle(message);

        foreach (var postRequestHandler in postRequestHandlers)
        {
            await postRequestHandler.Handle(message, result);
        }

        return result;
    }
}

I register my preprocessors with autofac, for example:

builder.RegisterAssemblyTypes(Assembly.GetExecutingAssembly())
    .As(type => type.GetInterfaces()
        .Where(type => type.IsClosedTypeOf(typeof(IAsyncPreRequestHandler<>))))
    .InstancePerLifetimeScope();

At runtime, I get duplicate pre-processors. I have to filter out the duplicate set. I do not know why this is happening. If I comment on the registration, I do not receive any preprocessors, which indicates that I am not duplicating the registration elsewhere.

Update. Below is some information about the type that appears to be registered twice. Different class definitions:

Concrete handler

public class ClientEditorFormIdentifierValidationHandler 
: IAsyncPreRequestHandler<AddOrEditClientCommand>{}

Team class

public class AddOrEditClientCommand 
: IAsyncRequest<ICommandResult>{}

Command interface

public interface IAsyncRequest<out TResponse> { }

Answer 1

, , . Autofac Modules, .

MVC5 :

builder.RegisterAssemblyModules(Assembly.GetExecutingAssembly());

" " :

builder.RegisterModule<MediatorModule>();

, , ... DUH..