Is is possible to use Ninject on an EntityFramework Entity object?

Question

I'm not sure if this is possible, but I'd like to have a class that can be loaded and saved using Entity Framework which also uses Ninject to populate Interfaces with concrete implementations at run time.

I started with a constructor like this:

    public FancyObject(ICatProvider kitty)
    {
        this.kitty = kitty;
    }

This works as far as Ninject goes, we get a Cat - and it works for saving the entity to SQLServer using Entity Framework. However, it fails when trying to load the entity because Entity Framework needs a parameterless constructor.

So I tried putting it on a property like this:

    [Inject]
    public ICatProvider kitty { get; set; }

    public FancyObject()
    {
    }

This can load from the DB, but Kitty is always null.

All I have in the bindings is:

    kernel.Bind<ICatProvider>().To<FancyFileBasedCat>();

I'm guessing this is because I'm using the Entity Framework to create the entities and so Ninject isn't getting a look in.

Am I missing something obvious here? Is there a nice way to do this?

Answer 1

Your guess is right. Your property is null because:

"using the Entity Framework to create the entities and so Ninject isn't getting a look in."

However you can use the Kernel.Inject method (wiki) to inject dependencies to existing instances:

var fancyObject = db.GetFancyObject();
kernel.Inject(fancyObject);
// fancyObject.kitty should be filled in.

Entities having dependencies usually is a code smell and maybe you should rethink your design. There are lots of way to avoid dependencies in entities like:

• Passing the service when it is needed:

  public class FancyObject
  {
       public Result MethodWorkingWithCats(int somearg, ICatProvider kitty)
       {
            reuturn DoSoemThing(this, somearg, kitty)
       }
  }
  

• Create a FancyObjectService which dependy on the ICatProvider and works on/with FancyObject
• etc.