How to declare a generic constraint that is a generic type

Question

I have a two generic abstract types: Entity and Association.

Let's say Entity looks like this:

public class Entity<TId>
{ 
//...
}

and Association looks like this:

public class Association<TEntity, TEntity2>
{
//...
}

How do I constrain Association so they can be of any Entity?

I can accomplish it by the following:

public class Association<TEntity, TId, TEntity2, TId2>
     where TEntity : Entity<TId>
     where TEntity2: Entity<TId2>
{
//...
}

This gets very tedious as more types derive from Association, because I have to keep passing down TId and TId2. Is there a simpler way to do this, besides just removing the constraint?

Answer 1

This problem is usually solved by having your generic class (Entity<TId>, in this case) inherit from a common non-generic class.

public abstract class EntityBase
{

}

public class Entity<TId> : EntityBase
{

}

This will allow you to do:

public class Association<TEntity, TEntity2>
    where TEntity : EntityBase
    where TEntity2 : EntityBase
{

}

Edit

If having them inherit from a common class is an issue, then this could be easily done with an interface as well.