轉自:http://blog.csdn.net/yifei12315/article/details/6985194

///??

Hibernate:??

????///??

????雙向關聯就是有“一對多”和“多對一”兩個關聯組合而成德，在雙向關聯的兩端都知道對方是誰。??

??

????下面就開始演示這種關聯。??

??

????首先定義我們需要使用的POJO對象。??

??

????public?class?Member??

????{??

????????private?String?id;???

????????private?String?name;???

????????private?Integer?age;???

????????private?Set<Order>?orders?=?new?HashSet<Order>();//我知道Order對象??

????????……??

????}??

??

????public?class?Order??

????{??

????????private?Integer?id;???

????????private?String?name;???

????????private?String?num;???

????????private?Member?member;//我知道Member對象??

????????……??

????}??

??

????兩個POJO對應的映射文件分別為Member.hbm.xml和Order.hbm.xml。??

??

????Member.hbm.xml??

??

????<hibernate-mapping?package="org.louis.domain">???

????????<class?name="Member"?table="TEST_MEMBER">??

????????????<id?name="id"?column="ID">???

????????????????<generator?class="uuid.hex"></generator>???

????????????</id>???

????????????<property?name="age"?column="AGE"></property>???

????????????<property?name="name"?column="NAME"></property>???

????????????<set?name="orders"?cascade="all"?inverse="true">??

????????????????<!--設置inverse=”true”表示Member不在作為主控方，就是說不再由Member來維持關聯關系，??

????????????????而有Order方來維持關聯關系，這樣Order在持久化的時候會主動去獲取Member的主鍵值來作為自己??

????????????????的外鍵值。?在one-to-manay關聯關系中，一般將manay端設置為主控方（inverse=”false”），??

????????????????這樣將有助于改善性能。默認情況下inverse=”false”?-->???

????????????????<key?column="MEMBER_ID"></key>???

????????????????<one-to-many?class="Order"/>???

????????????</set>??

????????</class>???

????</hibernate-mapping>??

??

????Order.hbm.xml??

??

????<hibernate-mapping?package="org.louis.domain">???

????????<class?name="Order"?table="TEST_ORDER">???

????????????<id?name="id"?column="ID">???

????????????????<generator?class="native"></generator>???

????????????</id>???

????????????<property?name="name"?column="NAME"></property>???

????????????<property?name="num"?column="NUM"></property>???

????????????<many-to-one?name="member"?class="Member"?column="MEMBER_ID"></many-to-one>??

????</hibernate-mapping>??

??

????下面我們來進行測試。??

??

????a、插入數據??

??

????public?void?insert()??

????{???

????????Session?session?=?HibernateSessionFactory.getSessionFactory().getCurrentSession();???

????????session.beginTransaction();???

????????Member?m?=?new?Member();???

????????m.setAge(24);???

????????m.setName("Louis");??

??

????????Order?order?=?new?Order();??

????????order.setName("order?1");??

????????order.setNum("order?num?1");??

????????order.setMember(m);??

????????m.getOrders().add(order);??

??

????????session.save(m);???

????????session.getTransaction().commit();???

????}??

??

????查看Hibernate在后臺使用的SQL語句如下：??

??

????Hibernate:???

????????insert???

????????into???

????????????TEST_MEMBER???

????????????(AGE,?NAME,?ID)???

????????values???

????????????(?,??,??)???

????Hibernate:???

????????insert???

????????into???

????????????TEST_ORDER???

????????????(NAME,?NUM,?MEMBER_ID)???

????????values???

????????????(?,??,??)??

??

????僅僅就兩條語句，明顯比單向關聯的時候少了一條更新語句（把Order的外鍵進行更新為Menber的主鍵值）。??

??

????b、加載數據??

??????

????和單向關聯的區別在于，如果加載的是Order對象，那么它也知道和它關聯的對象。??

??

????c、刪除數據??

??????

????刪除數據和單向關聯時的刪除數據的區別在于，對Member及它的關聯對象Order加載后，不需要在更新Order的外鍵為NULL，而是緊跟著逐條刪除Order，最后刪除Member。??

? ? ??

轉載于:https://www.cnblogs.com/springside4/archive/2012/05/02/2481154.html

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