Hash table with two primary keys

Question

Using System.Collections how to create a collection with two primary keys ?

I mean new entries with the same combination are avoided but each key can be used with other keys (like combining two primary keys in SQL)

Answer 1

You can simply use a struct, example:

struct CompositeKey<T1,T2>
{
  public T1 Item1;
  public T2 Item2;
}

Then use that as the key.