When choosing the classes for TPrimaryKey, consider that the method GetHashCode() should return an integer value that is appropriate for storage in a collection. Additionally, you may want to use the IEquatable<T> interface to assist you with equality checks. You may not have a class for TValue that exposes the TPrimaryKey value. That is ok - it just limits some of your options for operations like the Remove method. Of course, Remove is a virtual method so you may provide your own implementation there.