如何映射非持久性用户定义的类，以便Hibernate将使用SQLQuery中的实例加载bean

I am new to hibernate and am having difficulty trying to get it to work for anything other than a direct table mapping scenario. Basically, I have a user defined Java class called: BookInvoice. This class is a non-persistent (not a db table) and uses columns from previously defined and Annotated) db tables. Every time I try to label it as an @Entity it tells me I cant because it is not an existing db table. How do I map it so that I dont get the I am new to hibernate and am having difficulty