Unity Container ResolutionFailedException when the mapping is correct in the config file

I was using a ServiceLocator which i was DIing with Unity

public ServiceLocator(IUserStore userStore, IProdcutsStore productsStore, ...etc) {}

public IUserStore UserStore 
{ 
    get { return userStore; }
}

This all worked fine, but I wanted lazy instantiation of the repositories as they have quite sparse use.

So my ServiceLocator now looks like

    public ServiceLocator(IUnityContainer container) {}

    public IUserStore UserStore 
    { 
        get { return (IUserStore)container.Resolve(typeof(IUserStore)); }
    }

   //  ...etc

I'm now getting a really unhelpful ResolutionFailedException error

Resolution of the dependency failed, type = "DomainModel.DataServices.Interface.IUserStore", name = "". Exception message is: The current build operation (build key Build Key[DomainModel.DataServices.Interface.IUserStore, null]) failed: The current type, DomainModel.DataServices.Interface.IUserStore, is an interface and cannot be constructed. Are you missing a type mapping? (Strategy type BuildPlanStrategy, index 3)

Telling me my interfa开发者_如何学Cce type cannot be instantiated because it is an interface is pretty pointless. I know it's an interface, that's why the container is supposed to be resolving it for me!

Anyway, the point to note here is that I know the type mapping in the config is fine, as when I was injecting the type interface directly instead of trying to lazy load, it resolved it with no problems.

What am I missing that means something somewhere has to change in order to lazy load this way?

Update: I am guessing what's happening here, is that when I DI the container into the ServiceLocator, the "main" container is instantiating a new container each time which is then not configured properly. I think maybe I need some way to specify that I was to pass this in as the container, rather than resolve it with a new instantiation.

You're going in a somewhat wrong direction... At first you've had a testable class that declared its dependencies in the constructor and you turned it into non-so-testable, asking for "something" inside a container... No good =(

You should either implement some factory interface for your expensive object and require it in the constructor, or (if you can) switch to Unity 2.0 and use the Automatic Factories:

public ServiceLocator(Func<IUserStore> userStoreBuilder)

//...

public IUserStore UserStore 
{ 
   get { return userStoreBuilder(); }
}

If you want to only create the instance of that object once, you can add cahcing to that property, or with .NET 4.0 you can try asking Lazy in the constructor.

P.S. Oh, yes. And answering your particualr question =) If you still want to inject an instance of your container somewhere else, you need to first register it inside itself =)

container.RegisterInstance<IUnityContainer>(container);

Fix (see comments) DO NOT register a Unity container inside itself, this will cause StackOverflowException in container.Dispose(), the correct instance will be injected as a dependency without the registration.