Manual Mediator Registration Issue (v3.0.1->v5.0.1)

First: Thank you very much for this awesome project, it has inspired me a lot and structures my project architecture so much better. Thanks!

I am currently migrating from the old version 3.0.1 to the latest 5.0.1. Since I use the SimpleIoc from the MvvmLight framework, this was how I registered and setup MediatR in version 3:

var ioc = SimpleIoc.Default;
ioc.Register<IAsyncRequestHandler<DoJobRequest>, DoJobUseCase>();

var mediator = new Mediator(
          new SingleInstanceFactory(ioc.GetInstance),
          new MultiInstanceFactory(ioc.GetAllInstances)
);

await mediator.Send(new DoJobRequest());

With version 5.0.1 and the removal of the MultiInstanceFactory, I tried this (as described in the migration wiki):

var ioc = SimpleIoc.Default;
ioc.Register<IRequestHandler<DoJobRequest>, DoJobUseCase>();

var mediator = new Mediator(
          new ServiceFactory(ioc.GetInstance)
);

await mediator.Send(new DoJobRequest());

But I get the error, that the IEnumerable<IPipelineBehavior<...>> was not found… How should I setup MediatR now to get it going again?

Thank you very much.

[Brimce]

Hi, I’m in the same situation with splat container.

My solution :

 _dependencyResolver.RegisterLazySingleton<ServiceFactory>(() => (type =>
            {
                if (type.IsGenericType && type.GetGenericTypeDefinition() == typeof(IEnumerable<>))
                {
                    var enumerableType = type.GetGenericArguments()[0];

                    var pipelineInfo = enumerableType.GetGenericArguments()[0];

                    var requestType = pipelineInfo
                        .GetInterfaces()
                        .FirstOrDefault(type1 => type1.IsGenericType && type1.GetGenericTypeDefinition() == typeof(IRequest<>));

                    var responseType = requestType.GetGenericArguments()[0];

                    var typeArguments = new Type[2];
                    typeArguments[0] = requestType;
                    typeArguments[1] = responseType;
                    var pipelineType = typeof(GenericPipelineBehavior<,>).MakeGenericType(typeArguments);

                    var enumerableTypeResult = typeof(List<>).MakeGenericType(pipelineType);
                    var list = (IList) Activator.CreateInstance(enumerableTypeResult);

                    var pipeline = Activator.CreateInstance(typeof(GenericPipelineBehavior<,>).MakeGenericType(requestType, responseType));

                    list.Add(pipeline);

                    return list;
                }

                return _dependencyResolver.GetService(type);
            }));

Just replace _dependencyResolver with _ioc and add the folowing class:

 public class GenericPipelineBehavior<TRequest, TResponse> : IPipelineBehavior<TRequest, TResponse>
 {        
        public async Task<TResponse> Handle(TRequest request, CancellationToken cancellationToken, RequestHandlerDelegate<TResponse> next)
        {
            //log... "-- Handling Request"
            var response = await next();
            //log "-- Finished Request"
            return response;
        }
}

I Hope it can help !

[jbogard]

The problem that IServiceLocator is pretty much a dead end. A very old version of MediatR used IServiceLocator, but once that concept got abandoned, as did my usage of it.

Interestingly, the new ASP.NET Core DI is just IServiceProvider, which has existed in .NET since…forever. Everything else is extension methods on that, or extensions like IServiceScope