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Hibernate 关联映射 之 多对多 关联（二） 之拆分
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1、由問題引出一個多對多拆分成兩個多對一
??? 問題：Hibernate 關聯(lián)映射 之 多對多 關聯(lián)（一）中中間表只是一個存放用戶和角色的表，并無其他作用，如果客戶有其他的需求，該表就無法擴展。
2、問題解決過程：
用戶、角色 之間的關系拆分成用戶和用戶角色、角色和用戶角色的關系，即：兩個多對一的關系。
小技巧：如何去判斷多對一還是一對多對象，要從對象的角度來看，即：從一個對象的角度去看另一個對象。
用戶：
[java] view plain
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public?class?User?{????????private?int?id;??????private?String?name;??????private?String?password;??????private?Set<UserRole>?roles;??
用戶配置文件：
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<hibernate-mapping>??????<class?name="com.shangxuetang.User"?table="t_user">??????????<id?name="id">??????????????<generator?class="native"/>??????????</id>??????????<property?name="name"></property>??????????<property?name="password"></property>??????????<set?name="roles">??????????????<key?column="userID"></key>??????????????<one-to-many?class="com.shangxuetang.UserRole"/>??????????</set>??????</class>??</hibernate-mapping>??
角色：
[java] view plain
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public?class?Role?{??????private?int?id;??????private?String?name;??????private?Set<UserRole>?users;??
角色配置文件：
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<hibernate-mapping>??????<class?name="com.shangxuetang.Role"?table="t_role">??????????<id?name="id">??????????????<generator?class="native"/>??????????</id>??????????<property?name="name"></property>??????????<set?name="users">???????????????<key?column="roleID"></key>???????????????<one-to-many?class="com.shangxuetang.UserRole"/>??????????</set>??????</class>??</hibernate-mapping>??
用戶角色：
[java] view plain
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public?class?UserRole?{????????private?int?id;??????private?User?user;??????private?Role?role;??????private?Date?assignTime;????????????public?UserRole()?{}??????public?UserRole(User?u,Role?r)?{??????????this.user?=?u;??????????this.role?=?r;??????????this.assignTime?=?new?Date();??????}??
用戶角色配置文件：
[html] view plain
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<hibernate-mapping>??????<class?name="com.shangxuetang.UserRole"?table="t_userrole">??????????<id?name="id">??????????????<generator?class="native"/>??????????</id>??????????<property?name="assignTime"?type="date"></property>??????????<many-to-one?name="user"?column="userID"></many-to-one>??????????<many-to-one?name="role"?column="roleID"></many-to-one>????????????????</class>??</hibernate-mapping>??
測試示例代碼：
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public?void??testManytoManyChaiFen()?{??????????Session?session?=?HibernateUtil.getSession();??????????try?{??????????????session.beginTransaction();????????????????????????????User?u1?=?new?User("zhangsan");??????????????session.save(u1);??????????????User?u2?=?new?User("lisi");??????????????session.save(u2);????????????????????????????Role?r1?=?new?Role("adminstor");??????????????session.save(r1);??????????????Role?r2?=?new?Role("usualuser");??????????????session.save(r2);??????????????Role?r3?=?new?Role("VIPuser");??????????????session.save(r3);????????????????????????????UserRole?ur1?=?new?UserRole(u1,r1);??????????????session.save(ur1);????????????????????????????UserRole?ur2?=?new?UserRole(u1,r2);??????????????session.save(ur2);????????????????????????????UserRole?ur3?=?new?UserRole(u2,r1);??????????????session.save(ur3);????????????????????????????UserRole?ur4?=?new?UserRole(u2,r3);??????????????session.save(ur4);????????????????????????????UserRole?ur5?=?new?UserRole(u2,r2);??????????????session.save(ur5);????????????????????????????session.getTransaction().commit();??????????}catch(Exception?e)?{??????????????e.printStackTrace();??????????????session.getTransaction().rollback();??????????}finally?{??????????????session.close();??????????}??????}??
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