Question

I didn’t found short form for this question as subject…

Is it possible to inject already resolved instance’s property to dependency instance’s constructor?

My question arises from MVC tutorial, created in 2009.
It seems like it’s a cyclic dependency to me.

Anyway, can I:

• grab resolved ContactController (or its base Controller, Listing 3.) instance’s property ModelState
• and inject it to its dependency ContactService (Listing 4.) instances dependency ModelStateWrapper (Listing 7.)
• as constructor argument.

_service = new ContactManagerService(new ModelStateWrapper(this.ModelState)); (After Listing 8.)

How to accomplish above line with DI container?

I know that this validation that is happening in Service Layer can be done with data annotations or custom attributes, my question is not so much about design or architecture but possibility.

I have read Ninject wiki, some blog posts, answers, even found somewhat similar situations out there, but not exactly like this or was not able to figure out how to accomplish this or is it possible at all with Ninject.

BR,

Answer 1

No you can’t

To see the problem you must think about the order in which the objects are created

var modelStateWrapper = new ModelStateWrapper();
var service = new ContactService(modelStateWrapper);
var controller = new ContactController(service);

This means the modelstate wrapper is created longtime before the controller and therefore it is impossible to pass the model state to the ModelStateWrapper’s constructor. The only thing that is doable is to use Property Injection somewhere but this is only a workaround for the actual problem which is that you have a cyclic dependency.

The implementation also ties the service tightly to the controller. Consider using ModelValidators instead.