如何在NHibernate中的另一个子节点中将子对象字段用作复合键的一部分

I need to create a new Many-To-One relationship on my User entity which joins against another entity. The problem is the other entity has a compound key of which 1 field is a field in the User entity and the other is a field in another Many-To-One entity.I need to create a new Many-To-One relationship