code: public IdClass<Entity<T>> getOrCreateIdClass()
     {
        Node node = childNode.getOrCreate("id-class");
        IdClass<Entity<T>> idClass = new IdClassImpl<Entity<T>>(this, "id-class", childNode, node);
        return idClass;
     }
docs: If not already created, a new <code>id-class</code> element with the given value will be created.
  Otherwise, the existing <code>id-class</code> element will be returned.
  @return  a new or existing instance of <code>IdClass<Entity<T>></code>