Handling multiple MassTransit response types

Question

I needed to publish a message across the ESB (MassTransit) that will return a different type of object depending on how the message is processed. I wanted to implement this in a generic way so I could wire up other services with similar requirements in the same way.

Publish a request

public IGenericResponse<TPayload> PublishRequest<TMessage, TPayload>(TMessage message, Type[] potentialResponseTypes)
 where TMessage : class
{
 IGenericResponse<TPayload> commandResult = null;
 _bus.PublishRequest(message, c =>
 {
 foreach (Type responseType in potentialResponseTypes)
 {
 Type genericHandler = typeof(GenericHandler<,>).MakeGenericType(new[]{ responseType, typeof(TMessage)});
 var handler = new Action<object>(result =>
 {
 commandResult = (IGenericResponse<TPayload>) result;
 });
 Activator.CreateInstance(genericHandler, new object[] {c, handler});
 }
 c.SetTimeout(10.Seconds());
 });
 return commandResult;
}

Generic Handler to wire it up

internal class GenericHandler<TPayload, TMessage>
 where TMessage : class
 where TPayload : class
{
 public GenericHandler(InlineRequestConfigurator<TMessage> configurator, Action<object> handler)
 {
 configurator.Handle<GenericResponse<TPayload>>(handler);
 }
}

Thoughts?

• Nick Udell: What type is the c variable you get when you publish a request? Is this your response? If so there's a much simpler solution that needs way less reflection.

Answer 1

It's possible, providing c is your response from the bus, to do a lot of this without needing Reflection. Instead we can use a separate method and the joys of implicit typing to work out the type of TResponse for us.

Proposed solution

public IGenericResponse<TPayload> PublishRequest<TMessage, TPayload>(TMessage message, Type[] potentialResponseTypes)
 where TMessage : class
{
 IGenericResponse<TPayload> commandResult = null;
 _bus.PublishRequest(message, response =>
 {
 foreach (Type responseType in potentialResponseTypes)
 {
 var genericHandler = CreateHandler(response, message);
 }
 c.SetTimeout(10.Seconds());
 });
 return commandResult;
}
private GenericHandler<TResponse, TMessage> CreateHandler<TResponse,TMessage>(TResponse response, TMessage message)
{
 var handler = new Action<object>(result =>
 {
 commandResult = (IGenericResponse<TPayload>) result;
 });
 return new GenericHandler<TResponse, TMessage>(response, handler);
}