c# - Ninject does not trigger method when binding to method?

Question

The ViewModel depends on a list of MyObject which is bound to a Repository method that looks like it never gets called?

CompositionRoot

public sealed class CompositionRoot {
    public CompositionRoot(IKernel kernel) {
        if (kernel == null) throw new ArgumentNullException("kernel");
        this.kernel = kernel;
    }

    public void ComposeObjectGraph() {
        BindRepositoriesByConvention();
        BindDomainModel();
    }

    private void BindDomainModel() {
        kernel
            .Bind<IList<MyObject>>()
            .ToMethod(ctx => ctx.Kernel.Get<IMyObjectsRepository>().FindAllMyObjects())
            .WhenInjectedInto<MyObjectsManagementViewModel>();
    }

    private void BindRepositoriesByConvention() {
        kernel.Bind(s => s
            .FromThisAssembly()
            .SelectAllClasses()
            .EndingWith("Repository")
            .BindSelection((type, baseType) => type
                .GetInterfaces()
                .Where(iface => iface.Name.EndsWith("Repository"))));
    }

    private readonly IKernel kernel;
}

MyObjectsManagementViewModel

public class MyObjectsManagementViewModel {
    public MyObjectsViewModel(IList<MyObject> model) {
        if (model == null) throw new ArgumentNullException("model");
        Model = model;
    }

    public MyObject Current { get; set; }
    public IList<MyObject> Model { get; set; }
}

MyObjectsRepository

public class MyObjectsRepository 
    : NHibernateRepository<MyObject>
    , IMyObjectsRepository {
    public MyObjectsRepository(ISession session) : base(session) { }

    public IList<MyObject> FindAllMyObjects() { return GetAll(); }
}

The NHibernateRepository is an abstract class which exposes protected members allowing one to customize the method names through interfaces like IMyObjectsRepository to state a more domain friendly name, let's say.

The objects mappings work fine as NHibernate has properly created and updated the underlying database doing Domain-Driven Design.

The problem is definitely around my understanding or misuse (I believe) of Ninject while binding the list of MyObject to the Repository method.

• I've put a breakpoint to the FindAllMyObjects method, and it never gets hit?

• and the list of MyObjects being injected into the MyObjectsManagementViewModel constructor is always an empty one?

Answer 1

I think the issue here is you are binding to a type (IList<T>) that Ninject isn't expecting to resolve. the simplest solution is to instead bind to a Func that will return the object(s) you want.

for example:

kernel
    .Bind<Func<IList<MyObject>>>()
    .ToMethod(ctx => () => ctx.Kernel.Get<IMyObjectsRepository>().FindAllMyObjects())
    .WhenInjectedInto<MyObjectsManagementViewModel>();

then:

public MyObjectsViewModel(Func<IList<MyObject>> model) {
    if (model == null) throw new ArgumentNullException("model");
    Model = model();
}

this effectively does a lazy-load of the items from the repository when the MyObjectsViewModel object is constructed.

another alternative (which may be more clear and better design) would be to create a new interface like IMyObjectProvider, which is responsible only for finding and returning the correct data. then that interface would be injected into your viewmodel instead of the actual model objects.