Autofac - Register multiple decorators

Question

Given the following:

public interface ICommandHandler<in TCommand>
{
    void Handle(TCommand command);
}

public class MoveCustomerCommand
{

}

public class MoveCustomerCommandHandler : ICommandHandler<MoveCustomerCommand>
{
    public void Handle(MoveCustomerCommand command)
    {
        Console.WriteLine("MoveCustomerCommandHandler");
    }
}

public class TransactionCommandHandlerDecorator<TCommand> : ICommandHandler<TCommand>
{
    private readonly ICommandHandler<TCommand> _decorated;

    public TransactionCommandHandlerDecorator(ICommandHandler<TCommand> decorated)
    {
        _decorated = decorated;
    }

    public void Handle(TCommand command)
    {
        Console.WriteLine("TransactionCommandHandlerDecorator - before");
        _decorated.Handle(command);
        Console.WriteLine("TransactionCommandHandlerDecorator - after");
    }
}

public class DeadlockRetryCommandHandlerDecorator<TCommand> : ICommandHandler<TCommand>
{
    private readonly ICommandHandler<TCommand> _decorated;

    public DeadlockRetryCommandHandlerDecorator(ICommandHandler<TCommand> decorated)
    {
        _decorated = decorated;
    }

    public void Handle(TCommand command)
    {
        Console.WriteLine("DeadlockRetryCommandHandlerDecorator - before");
        _decorated.Handle(command);
        Console.WriteLine("DeadlockRetryCommandHandlerDecorator - after");
    }
}

I can decorate the MoveCustomerCommandHandler with a TransactionCommandHandlerDecorator using the following code:

var builder = new ContainerBuilder();

builder.RegisterAssemblyTypes(typeof(MoveCustomerCommandHandler).Assembly)
    .As(type => type.GetInterfaces()
    .Where(interfaceType => interfaceType.IsClosedTypeOf(typeof(ICommandHandler<>)))
    .Select(interfaceType => new KeyedService("commandHandler", interfaceType)));

builder.RegisterGenericDecorator(
        typeof(TransactionCommandHandlerDecorator<>),
        typeof(ICommandHandler<>),
        fromKey: "commandHandler");

var container = builder.Build();

var commandHandler = container.Resolve<ICommandHandler<MoveCustomerCommand>>();
commandHandler.Handle(new MoveCustomerCommand());

Which will output :

TransactionCommandHandlerDecorator - before  
MoveCustomerCommandHandler 
TransactionCommandHandlerDecorator - after 

How can I also decorate the TransactionCommandHandlerDecorator with the DeadlockRetryCommandHandlerDecorator, to generate the following output

DeadlockRetryCommandHandlerDecorator- before
TransactionCommandHandlerDecorator - before  
MoveCustomerCommandHandler 
TransactionCommandHandlerDecorator - after 
DeadlockRetryCommandHandlerDecorator- after

Answer 1

@nemesv has already answered this question, however I just thought I'd add that you can add some simple helper methods to make wiring up lots of generic decorators less painful in Autofac:

    private static void RegisterHandlers(
        ContainerBuilder builder, 
        Type handlerType,
        params Type[] decorators)
    {
        RegisterHandlers(builder, handlerType);

        for (int i = 0; i < decorators.Length; i++)
        {
            RegisterGenericDecorator(
                builder,
                decorators[i],
                handlerType,
                i == 0 ? handlerType : decorators[i - 1],
                i != decorators.Length - 1);
        }
    }

    private static void RegisterHandlers(ContainerBuilder builder, Type handlerType)
    {
        builder.RegisterAssemblyTypes(Assembly.GetExecutingAssembly())
            .As(t => t.GetInterfaces()
                    .Where(v => v.IsClosedTypeOf(handlerType))
                    .Select(v => new KeyedService(handlerType.Name, v)))
            .InstancePerRequest();
    }

    private static void RegisterGenericDecorator(
        ContainerBuilder builder,
        Type decoratorType,
        Type decoratedServiceType,
        Type fromKeyType,
        bool hasKey)
    {
        var result = builder.RegisterGenericDecorator(
           decoratorType,
           decoratedServiceType,
           fromKeyType.Name);

        if (hasKey)
        {
            result.Keyed(decoratorType.Name, decoratedServiceType);
        }
    }

If you paste those methods into the place you're configuring Autofac, then you can just do this:

    RegisterHandlers(
        builder, 
        typeof(ICommandHandler<>),
        typeof(TransactionCommandHandlerDecorator<>),
        typeof(ValidationCommandHandlerDecorator<>));

And it will wire up all your command handlers and add the decorators in the order given.

Answer 2

You just need to register your "TransactionCommandHandlerDecoratored" ICommandHandler as a Keyed service and use that new key when registering your second DeadlockRetryCommandHandlerDecorator:

builder.RegisterGenericDecorator(
        typeof(TransactionCommandHandlerDecorator<>),
        typeof(ICommandHandler<>),
        fromKey: "commandHandler")
        .Keyed("decorated", typeof(ICommandHandler<>));

builder.RegisterGenericDecorator(
        typeof(DeadlockRetryCommandHandlerDecorator<>),
        typeof(ICommandHandler<>),
        fromKey: "decorated");

And you will get the following output:

DeadlockRetryCommandHandlerDecorator - before
TransactionCommandHandlerDecorator - before
MoveCustomerCommandHandler
TransactionCommandHandlerDecorator - after
DeadlockRetryCommandHandlerDecorator - after