System.InvalidOperationException with KeyedServices in .NET 8

[kl1mm]

Hi, I'm currently playing with the new .NET 8 Preview 7 that came out a few days ago.

When I add a KeyedService to the DI container, it causes a System.InvalidOperationException thrown by MediatR.Registration.ServiceRegistrar.RegisterBehaviorIfImplementationsExist.

It seems that the ImplementationType property of ServiceDescriptor is accessed which is not allowed in the case of a "keyed" ServiceDescriptor.

maybe this helps to prepare MediatR for .NET8 KeyedServices?

cheers mMilk

Example to reproduce

var builder = WebApplication.CreateBuilder(args);

builder.Services.AddKeyedSingleton<MyService>("mykey");

// causes System.InvalidOperationException
builder.Services.AddMediatR(cfg =>
{
    cfg.RegisterServicesFromAssembly(typeof(Program).Assembly);
}); 

var app = builder.Build();

app.MapGet("/", (MyService svc) => svc.SayHello());
app.Run();

public class MyService
{
    public string SayHello() => "Hello";
}

Unhandled exception. System.InvalidOperationException: This service descriptor is keyed. Your service provider may not support keyed services. at Microsoft.Extensions.DependencyInjection.ServiceDescriptor.ThrowKeyedDescriptor() at Microsoft.Extensions.DependencyInjection.ServiceDescriptor.get_ImplementationType() at MediatR.Registration.ServiceRegistrar.<>c.b__12_0(ServiceDescriptor service) at System.Linq.Enumerable.SelectIListIterator2.MoveNext() at System.Linq.Enumerable.OfTypeIterator[TResult](IEnumerable source)+MoveNext() at System.Linq.Enumerable.SelectManySingleSelectorIterator2.MoveNext() at System.Linq.Enumerable.WhereSelectEnumerableIterator2.MoveNext() at System.Linq.Enumerable.Any[TSource](IEnumerable1 source, Func2 predicate) at MediatR.Registration.ServiceRegistrar.RegisterBehaviorIfImplementationsExist(IServiceCollection services, Type behaviorType, Type subBehaviorType) at MediatR.Registration.ServiceRegistrar.AddRequiredServices(IServiceCollection services, MediatRServiceConfiguration serviceConfiguration) at Microsoft.Extensions.DependencyInjection.ServiceCollectionExtensions.AddMediatR(IServiceCollection services, MediatRServiceConfiguration configuration)

[jbogard]

How would MediatR support keyed services? Typically when I use keyed services, I don't inject them. I instead resolve them directly from the composition root (the scoped IServiceProvider).

[jbogard]

Ah just adding a keyed service causes this issue? That seems strange, that an accessor throws this exception.

[jbogard]

Yep, this is what broke it: https://github.com/dotnet/runtime/pull/87183/files#diff-90a4b966bf74781df1f355057ad5adca90af0211e46c659965ce745fb0594b5dR157

I don't support keyed services, so I suppose I'll have to explicitly check to see if it's a keyed service and skip them. Annoying.

[kl1mm]

Hey @jbogard, yes it's not that MediatR supports Keyedservices but that the two can coexist in one application.

When I´m right ServiceDescriptor class has a property called IsKeyedService - maybe this helps.

mMilk

[jbogard]

Yeah that's what I'll have to do. Luckily that property is public!

[github-actions[bot]]

This issue is stale because it has been open 60 days with no activity. Remove stale label or comment or this will be closed in 14 days.

[davidfowl]

I just ran into this and came to file this issue 😄. Assembly scanning is convenient but often fragile 😞.

[Dulatr]

Are there any current workarounds to use both the keyed services feature and mediatr? It doesn't appear possible otherwise.

[jbogard]

@Dulatr use the MyGet feed. The latest is on RC1.

[jbogard]

Realized I didn't push, give it a few minutes and it'll be RC2.

[Dulatr]

@jbogard thanks for the response!

Sorry I've never used MyGet before, what's the feed url?

[jbogard]

There's a link in the readme but you can find it here: https://myget.org/gallery/mediatr-ci

If I was motivated I probably could have put prerelease packages up on NuGet. But like I said. Motivated.

[iatsuta]

Good afternoon, is there any news on solving the problem?

[lucasm-optimus]

I am facing the same issue but more strange is: I am not using any Keyed service in my Azure Functions project.