Generic types with MediatR

[dannyc02]

Hi @jbogard ,

I was wondering if it's possible to extend this framework to handle generic types in requests? Here's an example of what I was hoping to achieve:

mediator.Send(new CreateItemCommand<ItemType>(item))

public class CreateItemCommand<TItemType> : IRequest<T> where T: ISomeInterface

(Apologies if this isn't the correct place to ask this question.)

[jbogard]

That's possible today in MediatR, provides your handler factory knows how
to create it. StructureMap for example can do that.

On Wednesday, February 17, 2016, Dan C notifications@github.com wrote:

Hi @jbogard https://github.com/jbogard ,

I was wondering if it's possible to extend this framework to handle
generic types in requests? Here's an example of what I was hoping to
achieve:

mediator.Send(new CreateItemCommand(item))

public class CreateItemCommand : IRequest where T:
ISomeInterface

(Apologies if this isn't the correct place to ask this question.)

—
Reply to this email directly or view it on GitHub
#69.

[dannyc02]

Thanks for the speedy response @jbogard!

I've got this working by explicitly registering the in StructureMap, like so:

For<IRequestHandler<CreateItemCommand<Ping>, Ping>>().Use<CreateItemCommandHandler<Ping>>();

Is there a way to register this in StructureMap to handle all object types passed in? Something along these lines:

For<IRequestHandler<CreateItemCommand<T>, T>>().Use<CreateItemCommandHandler<T>>();

[khellang]

From 6 year younger @jbogard: Advanced StructureMap: connecting implementations to open generic types 😉

[dannyc02]

@khellang I'd attempted to use that method from that article without much luck :(
The article only has one 'level' deep of generics, like this:

public interface IHandler<TEvent>

where what I'm trying to achieve is this:

public interface IHandler<TEvent<TObjectType>>

Here's a snippet of what I've got in a single test - any help would be greatly appreciated.

[Test]
        public void ShouldResolveGenericHandler()
        {
            var container = new Container(cfg =>
            {
                cfg.Scan(scanner =>
                {
                    scanner.TheCallingAssembly();
                    scanner.IncludeNamespaceContainingType<Ping>();
                    scanner.WithDefaultConventions();
                    scanner.AddAllTypesOf(typeof(IRequestHandler<,>));
                    scanner.ConnectImplementationsToTypesClosing(typeof(IRequestHandler<,>));
                });
                cfg.For<SingleInstanceFactory>().Use<SingleInstanceFactory>(ctx => t => ctx.GetInstance(t));
                cfg.For<MultiInstanceFactory>().Use<MultiInstanceFactory>(ctx => t => ctx.GetAllInstances(t));
                cfg.For<IMediator>().Use<Mediator>();
            });

            var mediator = container.GetInstance<IMediator>();

            var response = mediator.Send(new CreateItemCommand<Ping>());

            response.Message.Should().NotBeNull();
        }


        public class CreateItemCommand<T> : IRequest<T>
        {

        }

        public class CreateItemCommandHandler<T> : IRequestHandler<CreateItemCommand<T>, T>
        {
            public T Handle(CreateItemCommand<T> message)
            {
                return default(T);
            }
        }

When looking at WhatDoIHave() - I can see the IRequestHandler in there:

IRequestHandler<CreateItemCommand<T>, T> MediatR Transient CreateItemCommandHandler<T> (Default)

However, when calling it, I get the following error:
----> StructureMap.StructureMapConfigurationException : No default Instance is registered and cannot be automatically determined for type 'IRequestHandler<CreateItemCommand<Ping>, Ping>'

Any ideas how to configure this with structuremap please @jbogard @khellang?

[jbogard]

I think you'll have to ask the StructureMap people on this one. But likely
you'll need to create a custom type scanner.

On Thursday, February 18, 2016, Dan C notifications@github.com wrote:

@khellang https://github.com/khellang I'd attempted to use that method
from that article without much luck :(
The article only has one 'level' deep of generics, like this:

public interface IHandler

where what I'm trying to achieve is this:

public interface IHandler<TEvent>

Here's a snippet of what I've got in a single test - any help would be
greatly appreciated.

[Test]
public void ShouldResolveGenericHandler()
{
var container = new Container(cfg =>
{
cfg.Scan(scanner =>
{
scanner.TheCallingAssembly();
scanner.IncludeNamespaceContainingType();
scanner.WithDefaultConventions();
scanner.AddAllTypesOf(typeof(IRequestHandler<,>));
scanner.ConnectImplementationsToTypesClosing(typeof(IRequestHandler<,>));
});
cfg.For().Use(ctx => t => ctx.GetInstance(t));
cfg.For().Use(ctx => t => ctx.GetAllInstances(t));
cfg.For().Use();
});

        var mediator = container.GetInstance<IMediator>();

        var response = mediator.Send(new CreateItemCommand<Ping>());

        response.Message.Should().NotBeNull();
    }


    public class CreateItemCommand<T> : IRequest<T>
    {

    }

    public class CreateItemCommandHandler<T> : IRequestHandler<CreateItemCommand<T>, T>
    {
        public T Handle(CreateItemCommand<T> message)
        {
            return default(T);
        }
    }

When looking at WhatDoIHave() - I can see the IRequestHandler in there:

IRequestHandler<CreateItemCommand, T> MediatR Transient
CreateItemCommandHandler (Default)

However, when calling it, I get the following error:
----> StructureMap.StructureMapConfigurationException : No default
Instance is registered and cannot be automatically determined for type
'IRequestHandler<CreateItemCommand, Ping>'

Any ideas how to configure this with structuremap please @jbogard
https://github.com/jbogard @khellang https://github.com/khellang?

—
Reply to this email directly or view it on GitHub
#69 (comment).

[dannyc02]

Ok thanks @jbogard.

Will report back findings.

[jeremydmiller]

@dannyc02 See this http://structuremap.github.io/generics/ and this http://structuremap.github.io/registration/auto-registration-and-conventions/. I'd urge you to be cautious about doing this though. You could easily get into a situation where the team just isn't going to be able to unravel the very fancy generics auto-registrations.

[dannyc02]

@jeremydmiller thanks for the info, really helped.

I managed to get it working using a custom convention, gist here: https://gist.github.com/dannyc02/6d42b90154d8478dc6fd