Allow registration of specific message handlers

[binarymash]

Hey @gautema,

Thanks for the effort you've put into CQRSlite. I've been using it for the last few months on a personal project and it's saved me a lot of time and effort. However, one thing that caused me some pain was how handlers are registered in RouteRegistrar. I have a suggestion for how this could be improved.

At the moment, the only option available is to register all the handlers in the same assembly as message type(s) I pass into RouteRegistrar.Register(...). This causes me problems because, in my use case, I don't want to register all the handlers in my code; I have a number of different handlers that might or might not be used, depending on the particular configuration of my code. I want to choose exactly which handlers I want to register. At the moment, the only option I have using is to split my handlers into multiple different assemblies.

To work around this limitation, I implemented my own code to allow me to explicitly pass in the handlers I want to register. So, now I can do this...

var handlers = new List<Type>(){
  // the message handlers I want to register
}

myRouteRegistrar.RegisterHandlers(handlers)

My implementation is much more complex than it ought to be; some of the registration code in CQRSlite is internal, so I need to use reflection and also copy and paste some of the code into my own project.

Implementing this directly in CQRSlite would be much simpler. I envisage that we'd make the following changes to RouteRegistrar:

1. Mark RouteRegistrar.Register(params Type[] typesFromAssemblyContainingMessages) as obsolete
2. Add a new method, RouteRegistrar.RegisterAllHandlersInSameAssemblyAs(params Type[] typesFromAssemblyContainingMessages) that behaves the same as the current RouteRegistrar.Register(...)
3. Add a new method, RouteRegistrar.RegisterHandlers(params Type[] messageHandlers) that registers the specific handlers passed in.

Is this something that you think would be useful to get into the CQRSlite code base? If so, I'll look at implementing this.

[gautema]

Hi, and thanks for the feedback.

I have always just though of the RouteRegistar as a convenient way to register all at the same time. In your case, I would look at just registering them directly on the Router manually. If that becomes to cumbersome, I guess don't think adding a new method in the RouteRegistar would do any harm. I have to think a bit about the renaming and deprecation as I'd like to avoid it if possible. If you make pull request for it with tests, I can get it in to the code during next week.

[binarymash]

Hmm.. I wonder if I've misunderstood the registration process and made things more complex than it needs to be :)

Ok, let me check my code - I'll get back to you.

[binarymash]

Ok, I've looked through the code... There's quite a lot of boilerplate code to register each handler - basically copying much of RouteRegistrar.InvokeHandler to create the delegates to pass into IHandlerRegistrar.RegisterHandler.

So, I think it's worth having something in CQRSlite... I've had a go at implementing it, and it's actually a very small change. Seems to work ok for me, I'll create a pull request shortly.

[gautema]

Fix in 0.20.0