Mediator pipline behaviors registration

Question

I have a asp.net core web api project with Mediatr 3.0.1 and structureMap.Microsoft.DependencyInjection 1.4.0.

I would like to use the pre and post-processing behavior. The IPipelineBehavior works as expected but thoese 2 don't:

public class PostProcessingBehavior<TRequest, TResponse> : IRequestPostProcessor<TRequest, TResponse>
{
    public Task Process(TRequest request, TResponse response)
    {
        LogTo.Info("Post processing: All Done");
        return Task.FromResult(0);
    }
}

public class PreProcessingBehavior<TRequest>: IRequestPreProcessor<TRequest>
{
    public Task Process(TRequest request)
    {
        // add validators here
        LogTo.Info("Pipline preprocessing happens");

        return Task.FromResult(0);
    }
}

Container registration:

private IServiceProvider ConfigureIoC(IServiceCollection services)
{
    var container = new Container();
    container.Configure(cfg =>
    {
        cfg.Scan(scanner =>
        {
            scanner.AssemblyContainingType(typeof(Startup));
            scanner.AssemblyContainingType(typeof(CustomerGetHandler));
            scanner.ConnectImplementationsToTypesClosing(typeof(IRequestHandler<>)); // Handlers with no response
            scanner.ConnectImplementationsToTypesClosing(typeof(IRequestHandler<,>)); // Handlers with a response
            scanner.ConnectImplementationsToTypesClosing(typeof(IAsyncRequestHandler<>)); // Async handlers with no response
            scanner.ConnectImplementationsToTypesClosing(typeof(IAsyncRequestHandler<,>)); // Async Handlers with a response
            scanner.ConnectImplementationsToTypesClosing(typeof(INotificationHandler<>));
            scanner.ConnectImplementationsToTypesClosing(typeof(IAsyncNotificationHandler<>));
            scanner.WithDefaultConventions();
        });

        cfg.For(typeof(IPipelineBehavior<,>)).Add(typeof(PreProcessingBehavior<>));
        cfg.For(typeof(IPipelineBehavior<,>)).Add(typeof(LoggingBehavior<,>));
        cfg.For(typeof(IPipelineBehavior<,>)).Add(typeof(PostProcessingBehavior<,>));

        cfg.For<SingleInstanceFactory>().Use<SingleInstanceFactory>(ctx => t => ctx.GetInstance(t)).ContainerScoped();
        cfg.For<MultiInstanceFactory>().Use<MultiInstanceFactory>(ctx => t => ctx.GetAllInstances(t)).ContainerScoped();
        cfg.For<IMediator>().Use<Mediator>();

        cfg.Populate(services);
    });

    return container.GetInstance<IServiceProvider>();
}

The error says:
ArgumentOutOfRangeException: Specified argument was out of the range of valid values. Parameter name: instance 'PostProcessingBehavior' with ReturnType PostProcessingBehavior cannot be cast to IPipelineBehavior

this is from the example: https://github.com/jbogard/MediatR/blob/master/samples/MediatR.Examples.StructureMap/Program.cs

Answer 1

Looking at the example you have linked to you seem to have confused the interfaces.

You have implemented IRequestPostProcessor & IRequestPreProcessor not an IPipelineBehavior.

So you should be registering to the interfaces you are implementing:

cfg.For(typeof(IRequestPreProcessor<>)).Add(typeof(PreProcessingBehavior<>));
cfg.For(typeof(IRequestPostProcessor<,>)).Add(typeof(PostProcessingBehavior<,>));

From reading the documentation, you may also need to register the following

cfg.For(typeof(IPipelineBehavior<,>)).Add(typeof(RequestPreProcessorBehavior<,>));
cfg.For(typeof(IPipelineBehavior<,>)).Add(typeof(RequestPostProcessorBehavior<,>));