Question

I’ve been using Ninject for a short time, and I’m trying to figure out how to do something that I’ve done in Unity with app.config/web.config entries.

I’m pretty sure this is simple, just haven’t found the best way to implement it, and of course Ninject doesn’t have the greatest documentation around.

I want to have different implementations for an interface, with no change in the code – the specific application knows which implementation to use.

For example, when I used Unity, I would have a live app and a unit test library, using different data libraries. So:

var repo = IoC.Get<IRepository>();

would return a RealRepository in my live app, and a FakeRepository in my unit tests. I would simply map the classes in my app.config or web.config.

In Ninject, since you define the mappings in the code, there doesn’t seem to be a way to decide which implementations (or which module) you use, except in the code – but of course the whole purpose is I don’t want to have to specifically state which implementation I want to use.

Is there a good way to do this? The only way I can think is to dynamically choose the NinjectModule implementation from the config file, but that just doesn’t feel right.

Answer 1

Is sounds like you are missusing an IoC container as Service Locator. This gives you many problems. One of it is that testing is much more difficult. I suggest to do it right instead and do constructor injsction instead of service location.

This means instead of

public class MyClass
{
    public void Do()
    {
        var repo = IoC.Get<IRepository>();
        ....
    }
}

You do

public class MyClass
{
    private IRepository repo;
    public MyClass(IRepository repo)
    {
        this.repo = repo;
    }

    public void Do()
    {
        ....
    }
}

There is just one Get for the root of your application. Everything else is passed through constructors.

It makes testing really simple:

var testee = new MyClass(new Mock<IRepository>());