Hibernate 中 元素的inverse 属性分析

试验背景:

表:

create table order_7( id number primary key, order_number varchar2(30), customer_id number) alter table order_7 drop column customer_id alter table order_7 add constraint customer_id_fk customer_id references customer(id); CREATE TABLE CUSTOMERS ( ID NUMBER, NAME VARCHAR2(20) NOT NULL ENABLE, PRIMARY KEY (ID) ENABLE )

Customer.java

package com.liuxi.examples; import java.util.HashSet; import java.util.Set; import com.sun.org.apache.bcel.internal.generic.NEW; public class Customer { private Long id; private String name; private Set<Order> orders = new HashSet<Order>(); public Long getId() { return id; } public void setId(Long id) { this.id = id; } public String getName() { return name; } public void setName(String name) { this.name = name; } public Set<Order> getOrders() { return orders; } public void setOrders(Set<Order> orders) { this.orders = orders; } }

Order.java

package com.liuxi.examples; import java.util.HashSet; import java.util.Set; import com.sun.org.apache.bcel.internal.generic.NEW; public class Customer { private Long id; private String name; private Set<Order> orders = new HashSet<Order>(); public Long getId() { return id; } public void setId(Long id) { this.id = id; } public String getName() { return name; } public void setName(String name) { this.name = name; } public Set<Order> getOrders() { return orders; } public void setOrders(Set<Order> orders) { this.orders = orders; } }

Customer.hbm.xml

<hibernate-mapping> <class name="com.liuxi.examples.Customer" table="CUSTOMERS" schema="HIBERNATE"> <id name="id" column="ID" type="java.lang.Long"> <generator class="increment"/> </id> <property name="name" column="NAME" type="java.lang.String"/> <set name="orders" cascade="save-update delete" inverse="true" > <key column="CUSTOMER_ID"/> <one-to-many class="com.liuxi.examples.Order"/> </set> </class> </hibernate-mapping>

Order.hbm.xml

<hibernate-mapping> <class name="com.liuxi.examples.Order" table="ORDER_7" schema="HIBERNATE"> <id name="id" column="ID" type="java.lang.Long"> <generator class="increment"/> </id> <property name="orderNumber" column="ORDER_NUMBER" type="java.lang.String"/> </class> </hibernate-mapping>

级联保存与Customer对象相关的Order对象:

SessionFactory sessionFactory = HibernateSessionFactoryUtil .getSessionFactory(); Session session = sessionFactory.getCurrentSession(); Transaction tx = session.beginTransaction(); Order order = new Order(); order.setOrderNumber("1234567"); Customer customer = new Customer(); customer.setName("马云"); customer.getOrders().add(order); try { session.save(customer); // 级联保存与customer对象关联的order对象 tx.commit(); } catch (Exception e) { tx.rollback(); }

如果Customer.hbm.xml中set元素的属性inverse为true,则控制台输出的信息为:

Hibernate: select max(ID) from CUSTOMERS Hibernate: select max(ID) from ORDER_7 Hibernate: insert into HIBERNATE.CUSTOMERS (NAME, ID) values (?, ?) Hibernate: insert into HIBERNATE.ORDER_7 (ORDER_NUMBER, ID) values (?, ?)

如果Customer.hbm.xml中set元素的属性inverse为false(默认是false),则控制台输出的信息为:

Hibernate: insert into HIBERNATE.CUSTOMERS (NAME, ID) values (?, ?) Hibernate: insert into HIBERNATE.ORDER_7 (ORDER_NUMBER, ID) values (?, ?) Hibernate: update HIBERNATE.ORDER_7 set CUSTOMER_ID=? where ID=?

发现这时，多执行了一条update语句。Why?

inverse=false分析:

当修改了Customer 对象的属性:

customer.getOrders().addOrder(order)

Hibernate 一旦知道持久态对象customer的上面的属性发生变化，执行相应的SQL语句:

update
HIBERNATE.ORDER_7
set
CUSTOMER_ID=?
where
ID=?

但如果将inverse=true,则customer与order之间的关系的控制被反转了，

Hibernate 监测到Customer对象上的属性发生变化，并不会去更新与该Customer对象相关的order记录。因为控制被反转了，

one 的一方(Customer)你变你的，我(Order)不会因为你的变化而被Hibernate控制，因为控制反转了，控制权不在你Customer一方，哈哈。我(many 一方)独立了！！

这样一来，我们在应用程序开发过程中为了提高性能，最好是在“one"方把<set>元素的inverse属性设置为true.