如何使用Autofac将WCF服务实现注入另一个WCF服务

Question

I have multiple WCF Services hosted in IIS and configured with Autofac.

Global.asax

var builder = new ContainerBuilder();

builder.RegisterType<ServiceA>();
builder.RegisterType<ServiceB>();
builder.RegisterType<ServiceC>();

var container = builder.Build();
AutofacHostFactory.Container = container;

web.config

<system.serviceModel>
  ...
  <serviceHostingEnvironment aspNetCompatibilityEnabled="true" multipleSiteBindingsEnabled="true">
    <serviceActivations>
      <add service="ServiceA, MyServicesAssembly" relativeAddress="./ServiceA.svc" factory="Autofac.Integration.Wcf.AutofacServiceHostFactory, Autofac.Integration.Wcf" />
      <add service="ServiceB, MyServicesAssembly" relativeAddress="./ServiceB.svc" factory="Autofac.Integration.Wcf.AutofacServiceHostFactory, Autofac.Integration.Wcf" />
      <add service="ServiceC, MyServicesAssembly" relativeAddress="./ServiceC.svc" factory="Autofac.Integration.Wcf.AutofacServiceHostFactory, Autofac.Integration.Wcf" />
    </serviceActivations>
  </serviceHostingEnvironment>
<system.serviceModel>

Service Implementations

public class ServiceA : IServiceA 
{
    public ServiceA()
    {            
    }
}

public class ServiceB : IServiceB
{
    public ServiceB()
    {            
    }
}

public class ServiceC : IServiceC
{
    public ServiceC(IServiceA serviceA)
    {            
    }
}

As you can see, ServiceC is different from the others and need an implementation of IServiceA. Autofac can't resolve it, because there is no registration for IServiceA.

So I change the registration to this:

builder.RegisterType<ServiceA>().As<IServiceA>();

Autofac can now resolve ServiceC successfully, but the WCF hosting is not working anymore:

An exception of type 'System.ServiceModel.ServiceActivationException' occurred in mscorlib.dll but was not handled in user code

So my question is:

Is there a way that I can have both, a hosted WCF Service instance, and the possibility to pass a Service Implementation to another Service? All configured with AutoFac? I'm also thinking of a workaround, but everything that comes to my mind results in a huge effort. I know that these services needs to be refactored, so that there is no need to pass in another "service". But this is a different story.

Answer 1

If you want to expose a component as a set of services as well as using the default service, use the AsSelf method:

//...

builder.RegisterType<ServiceA>()
    .AsSelf() //<--
    .As<IServiceA>();

//...

This will associate the class and interface together so that IServiceA can be injected as needed and it will be resolved to ServiceA . This also allow the WCF to not break as ServiceA is registered.

Reference Autofac Documentation: Registration Concepts