两表通过中间表多对多关联用HQL查询
如有user表，role表，userrole表，3者之间的关系是，user表和role表通过userrole表多对多关联。 定义user类： [code="java"]public class user implements java.io.Serializable { private Integer userId; private String userName; private Set userrole= new HashSet(0); //get和set省略 }[/code] 定义role类： [code="java"]public role implements java.io.Serializable { private Integer roleId; private String roleName; private Set userrole= new HashSet(0); //get和set省略 }[/code] 定义userrole类： [code="java"]public userrole implements java.io.Serializable { private Integer userroleID; private role role; private user user; //get和set省略 }[/code] 对应的xml： [code="java"] <!--只捡关联部分--> <!--user--> <key><column name="userId" not-null="true"></column></key><one-to-many class="mo.hibernate.map.userrole"></one-to-many><!--role--><key><column name="roleId" not-null="true"></column></key><one-to-many class="mo.hibernate.map.userrole"></one-to-many><!--userrole--><many-to-one name="role" class="mo.hibernate.map.role" fetch="select"><column name="roleId" not-null="true"></column></many-to-one><many-to-one name="user" class="mo.hibernate.map.user" fetch="select"><column name="userId" not-null="true"></column></many-to-one> [/code] 问题是：如何用hql查找出角色为admin的用户的id和名字？ hql： [code="java"] select u.userId,u.userName from user u,userrole ur,role r where u.userID in(ur.user) and r.roleName='admin' and ur.userroleID in elements(r.userrole) [/code] 本例用到了in和in elements关键字，区别在于in elements用于set，in用于实例对象。