hibernate 关联映射（三） one to one(双向)

 继之前的工程，现在来看下如何实现双向映射。
就是用IdCard能找到Person，也能用Person找到IdCard
 
前面的IdCard和Person的实体类代码没有态度的变化，主要是因为要实现双向映射，所以要在两个类中分别持有另一方对象。
 
主要看下两个配置文件：

 

Person.hbm.xml

 

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC 
	"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
	"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
	<class name="com.mp.hibernate.Person" table="t_person">
		<id name="id">
			<generator class="foreign">
				<param name="property">idCard</param>
			</generator>
		</id>
		<property name="name"></property>
		<one-to-one name="idCard" constrained="true"></one-to-one>
	</class>
</hibernate-mapping>

 

这个文件与上一个工程没有变化，现在主要是添加Person到IdCard的映射，所以看下

IdCard.hbm.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC 
	"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
	"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
	<class name="com.mp.hibernate.IdCard" table="t_idcard">
		<id name="id">
			<generator class="native"></generator>
		</id>
		<property name="cardNo"></property>
		<one-to-one name="person"></one-to-one>
	</class>
</hibernate-mapping>

 

也就是说实现双向映射就在IdCard的配置文件中再添加一个one-to-one标签

<one-to-one name="person"></one-to-one>

 

再看下测试类：

package com.mp.hibernate;

import org.hibernate.Session;

import junit.framework.TestCase;

public class One2OneTest extends TestCase {
	public void testSave1() {
		Session session = null;
		try {
			session = HibernateUtils.getSession();
			session.beginTransaction();
			
			IdCard idCard = new IdCard();
			idCard.setCardNo("234589389894893384");
			
			Person person = new Person();
			person.setName("刘德华");
			person.setIdCard(idCard);
			
			//不会出现TransientObejectException异常
			//因为一对一主键关联映射中，默认了cascade属性
			session.save(person);
			
			session.getTransaction().commit();
		} catch (Exception e) {
			e.printStackTrace();
			session.getTransaction().rollback();
		} finally {
			HibernateUtils.closeSession(session);
		}
	}
	
	public void testLoad() {
		Session session = null;
		try {
			session = HibernateUtils.getSession();
			session.beginTransaction();
			
			Person person = (Person)session.load(Person.class, 1);
			
			System.out.println("person.name=" + person.getName());
			System.out.println("idcard.cardNo" + person.getIdCard().getCardNo());
			
			session.getTransaction().commit();
		} catch (Exception e) {
			e.printStackTrace();
			session.getTransaction().rollback();
		} finally {
			HibernateUtils.closeSession(session);
		}
	}
	
	public void testLoad2() {
		Session session = null;
		try {
			session = HibernateUtils.getSession();
			session.beginTransaction();
			
			IdCard idCard = (IdCard)session.load(IdCard.class, 1);
			
			System.out.println("\nidcard.cardNo = " + idCard.getCardNo());
			System.out.println("idcard.person.name = " + idCard.getPerson().getName());
			
			session.getTransaction().commit();
		} catch (Exception e) {
			e.printStackTrace();
			session.getTransaction().rollback();
		} finally {
			HibernateUtils.closeSession(session);
		}
	}
}

 

运行测试类的各个方法，看下Console里面的变化

 

运行了save1方法后的结果是：

Hibernate: insert into t_idcard (cardNo) values (?) 
Hibernate: insert into t_person (name, id) values (?, ?) 

  然后又运行了load方法：

Hibernate: select person0_.id as id1_0_, person0_.name as name1_0_ from t_person person0_ where person0_.id=? 
person.name=刘德华 
Hibernate: select idcard0_.id as id0_1_, idcard0_.cardNo as cardNo0_1_, person1_.id as id1_0_, person1_.name as name1_0_ from t_idcard idcard0_ left outer join t_person person1_ on idcard0_.id=person1_.id where idcard0_.id=? 
idcard.cardNo234589389894893384 

 再运行了load2方法:

Hibernate: select idcard0_.id as id0_1_, idcard0_.cardNo as cardNo0_1_, person1_.id as id1_0_, person1_.name as name1_0_ from t_idcard idcard0_ left outer join t_person person1_ on idcard0_.id=person1_.id where idcard0_.id=? 

idcard.cardNo = 234589389894893384 
idcard.person.name = 刘德华 

 

看下数据库：