Scanning generics for mediatr handlers

[atresnjo]

Hi. I have a generic mediatr request handler which looks like this:

  public class GetOneByIdHandler<T> : IRequestHandler<GetOneByIdRequest<T>, T> where T : IBaseEntity
    {
        private readonly IAsyncRepository<T> _asyncRepository;

        public GetOneByIdHandler(IAsyncRepository<T> asyncRepository)
        {
            _asyncRepository = asyncRepository;
        }

        public async Task<T> Handle(GetOneByIdRequest<T> request, CancellationToken cancellationToken)
        {
            return await _asyncRepository.GetOneByIdAsync(request.Id);
        }
    }

Right now I have to add the handler for every DTO manually. How can I automate this with Scrutor? Thanks!

services.AddTransient<IRequestHandler<GetOneByIdRequest<MyDto>, MyDto>, GetOneByIdHandler<MyDto>>();

[khellang]

Hey! 👋

You should be able to register using this pattern:

Scrutor/test/Scrutor.Tests/ScanningTests.cs

Lines 194 to 197 in 9f095b0

	Collection.Scan(scan => scan.FromAssemblyOf<IScopedService>()
	.AddClasses(classes => classes.AssignableTo(typeof(IQueryHandler<,>)))
	.AsImplementedInterfaces()
	.WithScopedLifetime());

[atresnjo]

Hey! 👋

You should be able to register using this pattern:

Scrutor/test/Scrutor.Tests/ScanningTests.cs

Lines 194 to 197 in 9f095b0

	Collection.Scan(scan => scan.FromAssemblyOf<IScopedService>()
	.AddClasses(classes => classes.AssignableTo(typeof(IQueryHandler<,>)))
	.AsImplementedInterfaces()
	.WithScopedLifetime());

Hey! Thanks for the help. But sadly that didnt work. I think I am missing something, but with that pattern how is scrutor supposed to know which DTOs to register?

[khellang]

Just look at the registrations in the services collection. It should be registered as IRequestHandler<,>, so you need to resolve IRequestHandler<GetOneByIdRequest<ApplicationUser>, ApplicationUser>.

[khellang]

If you want it registered as itself, you can use services.AddScoped(typeof(GetOneByIdHandler<>));

[atresnjo]

Just look at the registrations in the services collection. It should be registered as IRequestHandler<,>, so you need to resolve IRequestHandler<GetOneByIdRequest<ApplicationUser>, ApplicationUser>.

I checked the services collection and only the generic handler GetOneByIdHandler is missing. Other non-generic handlers are added.

[khellang]

Ah, I think I know what's happening now. Because GetOneByIdHandler<T> and IRequestHandler<in TRequest, TResponse> have different generic arity, the type is filtered out when trying to register using .AsImplementedInterfaces().

You either have to add .AsSelf() in addition, or just register the type explicitly, like this:

services.AddScoped(typeof(GetOneByIdHandler<>));

They should both end up doing the same (wrt. this specific type).

[atresnjo]

Ah, I think I know what's happening now. Because GetOneByIdHandler<T> and IRequestHandler<in TRequest, TResponse> have different generic arity, the type is filtered out when trying to register using .AsImplementedInterfaces().

You either have to add .AsSelf() in addition, or just register the type explicitly, like this:

services.AddScoped(typeof(GetOneByIdHandler<>));

They should both end up doing the same (wrt. this specific type).

Sadly not. ✌️ The IRequestHandler implementations which can be seen in the second screenshot are missing.

"Message": "Handler was not found for request of type MediatR.IRequestHandler2[KKH.MedDelivery.Application.Commands.Core.Requests.GetOneByIdRequest1[KKH.MedDelivery.Domain.MedicalPartner],KKH.MedDelivery.Domain.MedicalPartner]. Register your handlers with the container. See the samples in GitHub for examples."

Adding with scrutor:

Adding manually:

[Chris-ZA]

Hello. I am trying to do something very similar. @atresnjo, did you ever figure this out?

[atresnjo]

Hello. I am trying to do something very similar. @atresnjo, did you ever figure this out?

Hey @Chris-ZA

Sorry. I never figured it out. So if you ever figure it out feel free to post! :) thanks.

[julealgon]

@Chris-ZA / @atresnjo , did you consider using this native dependency injection package instead of scanning with Scrutor?

• MediatR.Extensions.Microsoft.DependencyInjection

[alexb5dh]

Encountered similar issue while trying to register open generic via Scan.

Using interfaces like that:

public interface ISingleton { }

public interface IAppCache<out TService>{}

public class AppCache<TService>: IAppCache<TService>, ISingleton {}

and registering via:

services.Scan(scan => scan.FromAssemblyOf<ISingleton>().AddClasses(c => c.AssignableTo<ISingleton>()).AsSelfWithInterfaces().WithSingletonLifetime())

trying to fetch the service:

provider.GetRequiredService<IAppCache<object>>()

doesn't work.

Version 3.3.0.
Does Scrutor really support open generics?

[khellang]

Does Scrutor really support open generics?

Absolutely, there a lots of tests in this repo showing that it works 😅

[alexb5dh]

Absolutely, there a lots of tests in this repo showing that it works 😅

Got it. Looks like I will need to dig deeper to the source code to figure out why my case doesn't wan't to 🙂