Autofac 6 - 将装饰器注册为也实现另一个接口

Question

before Autofac 6, I could do something like:

builder.RegisterType<ResourceStorageParallelOperationsLimitDecorator>()
       .As(new DecoratorService(typeof(IResourceStorage)))
       .As<INetworkQueueMetrics>();

In short, I could tell Autofac that all IResourceStorage instances should be decorated by ResourceStorageParallelOperationsLimitDecorator and that this decorator also offered the service INetworkQueueMetrics .

Now, in v6, if I do:

builder.RegisterDecorator<ResourceStorageParallelOperationsLimitDecorator,
                          IResourceStorage>()

I cannot continue the call with .As<>(...) .

And if I try to amend the registration of ResourceStorageParallelOperationsLimitDecorator like:

builder.RegisterDecorator<ResourceStorageParallelOperationsLimitDecorator,
                          IResourceStorage>();
builder.RegisterType<ResourceStorageParallelOperationsLimitDecorator>()
       .As<INetworkQueueMetrics>()
       .SingleInstance();

then this leads to INetworkQueueMetrics and IResourceStorage being resolved as two different instances of ResourceStorageParallelOperationsLimitDecorator , see the following test:

[Test]
public void INetworkQueueMetrics_resolves_to_the_same_instance_as_ResourceStorage()
{
  var container = BuildContainer();
  var resourceStorage = container.Resolve<IResourceStorage>();
  var networkMetrics = container.Resolve<INetworkQueueMetrics>();

  resourceStorage.Should().BeSameAs(networkMetrics); // <<<< FAILS
}

There are plenty of overrides for ContainerBuilder.RegisterDecorator() , maybe one of them would let me do what I need, but frankly their usage is not all that clear to me.

Any idea how I can get the semantics I want with Autofac v6?

Answer 1

What you're seeing is an intentional behavior. The point of a decorator is to decorate - it's basically a "value-add proxy." A decorator, in and of itself, doesn't expose a whole separate service - its sole purpose is to wrap something else. It only worked before somewhat accidentally - via a leaky abstraction in the way the fluent registration syntax functioned. That leak got "plugged" with the latest version.

If you need something to wrap a component and change the services exposed , that's an adapter and Autofac does have adapter support, too .

And, of course, if you need something more general purpose (like "log every call made to this thing"), you can use type interceptors .