Question

I’m using the Unity IoC framework and have a Bootstrapper.cs class in my host MVC layer to register all components. However in my architecture I have a ‘services’ layer below the MVC layer, that too uses DI and there are repository interfaces injected into it (repository interfaces are not used in the MVC layer – it has the services layer Interface injected into its Controllers).

So my question is the following: can I still register the repository interface to it’s concrete type in the MVC/UI layer for the entire app, or do I add another reference to Unity and create another Bootstrapper.cs class in my ‘services’ layer to define Interface types for that that specific layer uses?

Even if the answer is I can register the Interface in the UI layer, I’d still like to know the common practice too. The thing I don’t like about registering that type in the MVC/UI layer is I would have to add a reference to the Repository layer just to make the registration, even know it is not used in that layer. It’s used in the services layer.

Thanks!

Answer 1

Each application should have its own Composition Root, the place where you configure the application (see this answer for details).

It depends on the context, but generally speaking, if you split your container configuration among the layers you are going to make decisions about the configuration of your layers too close to the layers and you’are likely to lose the general view.

For example, in one of your business logic layers you’are registering a service:

container.RegisterType<ISercice1, MyImplementation1>(new PerThreadLifetime())

But when using that layer in a web application you could decide that a PerSession or PerRequest lifetime would be better lifetimes. This decisions should be in only one place and not spread through the layers.