INotificationHandler<T> where T is Interface does not handle publish calls

public class SubNotificationHandler : INotificationHandler<ISubNotification>
    {
        public async Task Handle(ISubNotification notification, CancellationToken cancellationToken)
        {
            //Do some
        }
    }

    public class NotificationHandler : INotificationHandler<Notification>
    {
        public async Task Handle(Notification notification, CancellationToken cancellationToken)
        {
             //Do some
        }
    }

I was trying to do something like this and on publish both Handle methods are called but if NotificationHandler does not exist then SubNotificationHandler.Handler is not called. Is there any way to fix this without creating an empty NotificationHandler? (Notification class is an implementation of ISubNotification)

[jbogard]

Feel free to upvote this PR:

https://github.com/dotnet/runtime/pull/39540

That adds constrained generics support to the built-in DI container.

[ArrowtheArcher]

Their relationship

    public class Notification : ISubNotification
    {
        public string Par { get; set; }

        public Notification(string par)
        {
            Par = par;
        }
    }

    public interface ISubNotification : INotification
    {
        string Par { get; set; }
    }

I tried constrained generic(if I am not mistaking) like this public class SubNotificationHandler<T> : INotificationHandler<T> where T: ISubNotification and it did help this case but I later encountered a problem. When I try to publish a notification that is not an implementation of ISubNotification I am getting this error

---

System.ArgumentException: GenericArguments[0], 'Mediator_Test.Shared.SecondNotification', on 'Mediator_Test.Shared.SubNotificationHandler`1[T]' violates the constraint of type 'T'. ---> System.TypeLoadException: GenericArguments[0], 'Mediator_Test.Shared.SecondNotification', on 'Mediator_Test.Shared.SubNotificationHandler`1[T]' violates the constraint of type parameter 'T'. at System.RuntimeTypeHandle.Instantiate(Type[] inst) at System.RuntimeType.MakeGenericType(Type[] instantiation) --- End of inner exception stack trace --- at System.RuntimeType.ValidateGenericArguments(MemberInfo definition, RuntimeType[] genericArguments, Exception e) at System.RuntimeType.MakeGenericType(Type[] instantiation) at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteFactory.TryCreateOpenGeneric(ServiceDescriptor descriptor, Type serviceType, CallSiteChain callSiteChain, Int32 slot) at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteFactory.TryCreateEnumerable(Type serviceType, CallSiteChain callSiteChain) at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteFactory.CreateCallSite(Type serviceType, CallSiteChain callSiteChain) at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteFactory.<>c__DisplayClass7_0.<GetCallSite>b__0(Type type) at System.Collections.Concurrent.ConcurrentDictionary`2.GetOrAdd(TKey key, Func`2 valueFactory) at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteFactory.GetCallSite(Type serviceType, CallSiteChain callSiteChain) at Microsoft.Extensions.DependencyInjection.ServiceLookup.ServiceProviderEngine.CreateServiceAccessor(Type serviceType) at System.Collections.Concurrent.ConcurrentDictionary`2.GetOrAdd(TKey key, Func`2 valueFactory) at Microsoft.Extensions.DependencyInjection.ServiceLookup.ServiceProviderEngine.GetService(Type serviceType, ServiceProviderEngineScope serviceProviderEngineScope) at Microsoft.Extensions.DependencyInjection.ServiceLookup.ServiceProviderEngineScope.GetService(Type serviceType) at MediatR.ServiceFactoryExtensions.GetInstances[T](ServiceFactory factory) at MediatR.Internal.NotificationHandlerWrapperImpl`1.Handle(INotification notification, CancellationToken cancellationToken, ServiceFactory serviceFactory, Func`4 publish) at MediatR.Mediator.PublishNotification(INotification notification, CancellationToken cancellationToken) at MediatR.Mediator.Publish[TNotification](TNotification notification, CancellationToken cancellationToken) at Mediator_Test.Server.Controllers.TargetController.Index() in C:\Users\Nadir_A\source\repos\Mediator Test\Mediator Test\Server\Controllers\TargetController.cs:line 27 at Microsoft.AspNetCore.Mvc.Infrastructure.ActionMethodExecutor.TaskOfIActionResultExecutor.Execute(IActionResultTypeMapper mapper, ObjectMethodExecutor executor, Object controller, Object[] arguments) at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.<InvokeActionMethodAsync>g__Logged|12_1(ControllerActionInvoker invoker) at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.<InvokeNextActionFilterAsync>g__Awaited|10_0(ControllerActionInvoker invoker, Task lastTask, State next, Scope scope, Object state, Boolean isCompleted) at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.Rethrow(ActionExecutedContextSealed context) at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.Next(State& next, Scope& scope, Object& state, Boolean& isCompleted) at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.InvokeInnerFilterAsync()