外键作为EF Code First中的主键？

Question

I need to map a relationship between 3 domain models in my domain, where as one of the domain models is the aggregate root of the relationship model.

public class Entity1 {
    public int Id { get; set; }
}

public class Entity2 {
    public int Id { get; set; }
}

public class SuperEntity {
    public int Id { get; set; }
    // bounded context for relationship classes
}

The relationship entity should look like this

public class Relationship {
    public int RelationshipId { get; set; }
    public Entity1 Entity1 { get; set; }
    public Entity2 Entity2 { get; set; }
}

Following this, the super entity should simply look like this:

public class SuperEntity {
    public int Id { get; set; }
    public ICollection<Relationship> Relationships { get; set; }
}

Now, one possibility to map this is to make the relationship a unique entity with it's own key and both entities inside the relationship unique indexes. But then the key only serves "for key purposes" without any meaningful value. Desireable would be a relationship table like this:

Table_Relationships
                  [  SuperEntity_Id // Foreign-key to SuperEntity
  PrimaryKey      [  Entity1_Id // Foreign-key to Entity1
                  [  Entity2_Id // Foreign-key to Entity2

Meaning that the primary key of Table_Relationships would be SuperEntity_Id+Entity1_Id+Entity2_Id.

Is it possible to map this in EF Code First?

Answer 1

Why not use DataAnnotations.KeyAttribute ( http://msdn.microsoft.com/library/system.componentmodel.dataannotations.keyattribute%28v=vs.110%29.aspx )? It's clear way to define complex primary key in domain model classes.