Autofac passing parameter to nested types

Question

I am using Autofac as my IoC in my WCF service. I have a situation where I want to pass an object to a nested type (ie a type that is not resolved directly, but when resolvi

Answer 1

IMHO, I think you're violating one of the principles of IOC in that a component should not need to know about the dependencies of it's dependencies. In your case, the container doesn't know that SomeBusinessObject has a dependency on User.

That being said, you may be able to leverage Autofac's Delegate Factories. You could manually register a Func<User, SomeBusinessObject> to hide the dependency chain details from the client code:

var builder = new ContainerBuilder();
builder.RegisterGeneric(typeof(Repository<>)).As(typeof(IRepository<>));
builder.RegisterGeneric(typeof(EventLogger<>)).As(typeof(IEventLogger<>));
builder.RegisterType<SomeBusinessObject>();

builder.Register<Func<User, SomeBusinessObject>>(c => {
    // Autofac should be able to resolve these Func<> automatically:
    var loggerFactory = c.Resolve<Func<User, IEventLogger<SomeLogEventType>>>();
    var sboFactory = c.Resolve<Func<IEventLogger<SomeLogEventType>, SomeBusinessObject>>();

        // Now we can chain the Funcs:
    return u => sboFactory(loggerFactory(u));
});

Now in your client code, you can do:

var currentUser = GetUserFromServiceContext();  
var sboFactory = lifetimeScope.Resolve<Func<User, SomeBusinessObject>>();
var bo = sboFactory(currentUser);

As an aside, I think the lamba/Func support is what makes Autofac the best IOC container. You can do some crazy powerful things if you know how to compose Funcs.