How to resolve constructor injection with multiple layers

Question

In my project I had a controller dependency on IRepositoryProvider among others.

public class HomeController : BaseController
{
    public HomeController(ISessionWrapper sessionWrapper,
                          IRepositoryProvider repositoryProvider,
                          IApplicationConfiguration applicationConfiguration)
        : base(sessionWrapper, repositoryProvider, applicationConfiguration)
    {}

    ...

}

IRepositoryProvider and its implementation live in a BLL layer. Another thing to note is that IRepositoryProvider has some parameters also. These are used to determine which connection strings to use (Environment*5 possible connections).

    public RepositoryProvider(string environment, IApplicationConfiguration applicationConfiguration)
    {
        _applicationConfiguration = applicationConfiguration;
        _environment = environment;
    }

This all works fine with two layers and this Ninject config.

kernel.Bind<IRepositoryProvider>()
      .To<RepositoryProvider>()
      .InRequestScope()
      .WithConstructorArgument("environment",    
                                context => context.Kernel.Get<ISessionWrapper>().CurrentEnvironment)
      .WithConstructorArgument("applicationConfiguration",
                                context => context.Kernel.Get<IApplicationConfiguration>());

My issue develops when I introduced a service layer. Instead of relying on IRepositoryProvider in my controllers for data access, I want to use the service layer. Ideally then I don't want to reference the BLL layer, and only the Service layer.

public class HomeService : IHomeService
{
    public IRepositoryProvider RepositoryProvider { get; private set; }

    public HomeService(IRepositoryProvider repositoryProvider)
    {
        RepositoryProvider = repositoryProvider;
    }
    ...
}

So my question is this: Is it possible for me to not reference both the Service and BLL layers from the MVC project? Or is this whole setup a massive code smell?

Thanks.

UPDATE: I suppose I should have said my ideal references. Web -> Service -> BLL. At the moment Web references both Service and BLL in order for Ninject to resolve everything.

UPDATE 2: Does this seem like a possible solution? How to tell Ninject to bind to an implementation it doesn't have a reference to

Answer 1

This is how I usually architect my MVC projects depending on requirements.

Presentation Layer > Service Layer > Business Layer > Data Access Layer.

Presentation Layer contains : ViewModels, Views, Controllers. (References the Service Layer, Ninject ddl)

Service Layer : WCF. (References the BAL, etc)

Business Layer : Contains what I call Orchestrators and their interfaces (References DAL, Domain)

Data Access Layer: Contains the Repositories and their Interfaces (References Domain)

Domain: Contains the POCO objects

Core : Where I actually install and configure Ninject (References the BAL, DAL, etc)

To Add Ninject to a another Project other than the Presentation Layer:

Add the following to Global.Asasx.cs:

DependencyResolver.SetResolver(new NinjectDependencyResolver());

Then create a new project sucche as core. Install Ninject there and add the following class:

You will need to reference the Ninject dll from the Presentation Layer

 public class NinjectDependencyResolver : IDependencyResolver {
    private IKernel kernel;

    public NinjectDependencyResolver() 
    {
        kernel = new StandardKernel();
        AddBindings();
    }

    public object GetService(Type serviceType) 
    {
        return kernel.TryGet(serviceType);
    }

    public IEnumerable<object> GetServices(Type serviceType) 
    {
        return kernel.GetAll(serviceType);
    }

    public IBindingToSyntax<T> Bind<T>() 
    {
        return kernel.Bind<T>();
    }

    public IKernel Kernel 
    {
        get { return kernel; }
    }

    private void AddBindings() 
    {
        //Add your Bindings here
    }

}

Answer 2

IRepositoryProvider and its implementation live in a BLL layer... Is it possible for me to not reference both the Service and BLL layers from the MVC project

With those two statement of yours the answer is NO, it is not possible for you "not" to reference those layers. The best approach of minimizing references is to separate your interfaces from the implementations. You can have for example the following:

The Domain Layer, contains your POCO and interface

• Product (a sample class)
• IRepository (an interface)

The Service Layer, contains the implementaion of your interfaces

• Have a reference to the Domain layer
• Implements IRepository (e.g. ProductRepository : IRepository)

Dependency Injection Layer

• Is aware of both the Domain and Service layers

The MVC Project

• Have a reference to the Domain layer to know about the POCOs and repository signatures
• Have a reference to the DI layer but doesn't know how it exactly works. So you can swap out DI framework later and everything will still work.

You can expand that layer as you see fit. You can insert the BLL layer in between the Domain and Service layer and you don't need reference it anywhere.