多對多關聯映射(雙向)

關聯映射方面的最后一篇了，我覺得映射文件的編寫是使用hibernate的基礎，而關聯映射又是基礎的基礎，所以這方面分的細一些，羅嗦一些，說明白就好，呵呵。

多對多關聯(雙向)，相對單向，在實體上就是一端也保持另一端的對象集合，在映射文件中也配置上。但是要注意兩邊配置文件中指定的外鍵一定要對應。

1.對象模型：

2.關系模型：

3.實體類：

Player.java

public?class?Player {?
??private?Integer id;?
??private?String name;?
??private?Set<Role> roles;?
??//一系列的setter.getter方法?
??@Override?
??public?String toString() {?
????return?"Player: "?+ name;?
??}?
}

? Role.java

public?class?Role {?
??private?Integer id;?
??private?String name;?
??private?Set<Player> players;?
??//一系列的setter.getter方法?
??@Override?
??public?String toString() {?
????return?"Role: "?+ name;?
??}?
}

4.映射文件：

?Player.hbm.xml

<class?name="com.sxt.hibernate.many2many.entity.Player"?table="sxt_hibernate_player">?
????<id?name="id"?length="4">?
??????<generator?class="native"></generator>?
????</id>?
????<property?name="name"?length="10"></property>?
?????
????<set?name="roles"?table="sxt_hibernate_player_role"?cascade="save-update">?
???????
??????<key?column="player_id"></key>?
???????
??????<many-to-many?class="com.sxt.hibernate.many2many.entity.Role"?column="role_id"></many-to-many>?
????</set>?
??</class>

? Role.hbm.xml

<class?name="com.sxt.hibernate.many2many.entity.Role"?table="sxt_hibernate_role">?
????<id?name="id"?length="4">?
??????<generator?class="native"></generator>?
????</id>?
????<property?name="name"?length="10"></property>?
????<set?name="players"?table="sxt_hibernate_player_role"?cascade="save-update">?
???????
??????<key?column="role_id"></key>?
???????
??????<many-to-many?class="com.sxt.hibernate.many2many.entity.Player"?column="player_id"></many-to-many>?
????</set>?
??</class>

5.hibernate配置文件：

參照上一篇。

6. 測試方法：

public?static?void?main(String[] args) {?
????Session session = HibernateUtils.getSession();?
????Transaction t = session.beginTransaction();?
????try?{?
??????/**?
????????* 測試插入數據?
????????*/????????
/*??????Player player1=new Player();?
??????player1.setName("姚明");?
????????
??????Player player2=new Player();?
??????player2.setName("詹姆斯");?
????????
??????Player player3=new Player();?
??????player3.setName("科比");?
????????
??????Role role1=new Role();?
??????role1.setName("中鋒");?
??????Set<Player> players1=new HashSet<Player>();?
??????players1.add(player1);?
??????players1.add(player2);?
??????role1.setPlayers(players1);?
????????
??????Role role2=new Role();?
??????role2.setName("后衛");?
??????Set<Player> players2=new HashSet<Player>();?
??????players2.add(player2);?
??????players2.add(player3);?
??????role2.setPlayers(players2);?
????????
??????session.save(role1);?
??????session.save(role2);*/?
????????
??????/**?
????????* 測試加載數據?
????????*/?
??????Role role=(Role)session.load(Role.class, 4);?
??????System.out.println(role);?
??????for(Iterator<Player> players=role.getPlayers().iterator();players.hasNext();){?
????????System.out.println(players.next());?
??????}?
??????t.commit();?
????}?catch?(HibernateException e) {?
??????e.printStackTrace();?
??????t.rollback();?
????}?finally?{?
??????HibernateUtils.closeSession(session);?
????}?
??}?
}?

? ? ?本文轉自NightWolves 51CTO博客，原文鏈接：http://blog.51cto.com/yangfei520/276187，如需轉載請自行聯系原作者

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