Problem getting an interface with IEnumerable<interface> working nicely

Question

Okay so I'm having a bit of trouble getting some interfaces to work. Basically I have an interface (A) and within that interface there is a property IEnumerable, where T is another interface (B). I have a bunch of entity framework models, some will implement A and others implement B. The models that implement A will have an IEnumerable where T is an implementation of B. I then have a bunch of methods I need to write that take A as a parameter and use the concrete implementation of B contained within the IEnumerable. The first, and most obvious attempt, looked like this:

public interface IA {
        public IEnumerable<B> BEnum {get; set;}
}

public interface IB {
        public string foo {get; set;}
        public int boo {get; set;}
}

public class ModelA : IA {
        public IEnumerable<ModelB> BEnum {get; set;}
}

public class ModelB : IB {
        public string foo {get; set;}
        public int boo {get; set;}
}

Except this doesn't work. In this attempt I get CS0738 because ModelA doesn't match the return type of the interface, which is fair enough. I tried reworking it like so:

public interface IA<T> where T: IB {
blah
}

public class ModelA : IA<ModelB> {
blah
}

And it looked like this was working except I can't figure out a way to get a method to accept IA as a parameter. Is this possible?

Answer 1

You can definetly have IA as a parameter of a method. Otherwise you can use generic methods. Here are some examples :

public class Foo
{
    public void Method(IA<IB> obj)
    { 
        /* Do something */
    } 

    public void GenericMethod_1<TB>(IA<TB> obj)
            where TB : ModelB
    { 
        /* Do something */
    } 

    public void GenericMethod_2<TA>(TA obj)
        where TA : ModelA
    { 
        /* Do something */
    } 

}

Method is the most general case where the method accepts any object implementing IA with any IB. The first generic method, GenericMethod_1, allows you to constraint the expected type T : IB that is used for IA. The second generic method, GenericMethod_2, accepts ModelA and any object derived from it.