How to register two WCF service contracts with autofac

Question

I have a WCF service that implements two service contracts...

public class MyService : IService1, IService2

and I am self-hosting the service...

host = new ServiceHost(typeof(MyService));

Everything was working fine when the service implemented only one service contract, but when I attempt to set up autofac to register both like this:

host.AddDependencyInjectionBehavior<IService1>(_container);
host.AddDependencyInjectionBehavior<IService2>(_container);

... it throws an exception on the second one, reporting:

The value could not be added to the collection, as the collection already contains an item of the same type: 'Autofac.Integration.Wcf.AutofacDependencyInjectionServiceBehavior'. This collection only supports one instance of each type.

At first glance I thought this was saying my two contracts were somehow being seen as the same type but on second reading I believe it is saying that the AutofacDependencyInjectionServiceBehavior is the type in question, i.e. I cannot use it twice!

And yet, I found this post that explicitly showed using it multiple times in a slightly different form:

foreach (var endpoint in host.Description.Endpoints)
{
  var contract = endpoint.Contract;
  Type t = contract.ContractType;
  host.AddDependencyInjectionBehavior(t, container);
}

Unfortunately, that gave the very same error message.

Is it possible to register more than one service contract on one service and, if so, how?

Answer 1

In fact you can register multiple endpoint for a single host with Autofac.

That is true that you cannot add multiple AutofacDependencyInjectionServiceBehavior but this behaviour iterates through all the endpoints and registers them in the ApplyDispatchBehavior method: source

In order to make this work you need to register your service AsSelf()

builder.RegisterType<MyService>();

Then you can configure your endpoint normally:

host = new ServiceHost(typeof(MyService));
host.AddServiceEndpoint(typeof(IService1), binding, string.Empty);
host.AddServiceEndpoint(typeof(IService2), binding, string.Empty);

And finally you need to call the AddDependencyInjectionBehavior with the sevicehost type itself:

host.AddDependencyInjectionBehavior<MyService>(container);

Here is a small sample project (based on the documentation) which demonstrates this behavior.