Hibernate关联关系映射之一对一关联关系

人和身份证之间就是一个典型的一对一关联关系。实现一对一关联关系映射的方式有两种一种是基于外键，一种是基于主键，下面我们先看基于外键的关联方式

首先看他们的实体类

Person类

package entity;public class Person {private Integer id;private String name;private IdCard idCard;public Integer getId() {return id;}public void setId(Integer id) {this.id = id;}public String getName() {return name;}public void setName(String name) {this.name = name;}public IdCard getIdCard() {return idCard;}public void setIdCard(IdCard idCard) {this.idCard = idCard;}}

然后看IdCard类

package entity;public class IdCard {private Integer id;private String number;private Person person;public Integer getId() {return id;}public void setId(Integer id) {this.id = id;}public String getNumber() {return number;}public void setNumber(String number) {this.number = number;}public Person getPerson() {return person;}public void setPerson(Person person) {this.person = person;}}

这里在Person类和IdCard类中分别有一个对方类型的属性。

然后看他们之间的关联关系映射，首先看Person.hbm.xml

<?xml version="1.0" encoding="utf-8"?><!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN""http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd"><hibernate-mapping>    <class name="entity.Person" table="Person" schema="MYHR">        <id name="id" type="int">            <column name="ID" />            <generator class="assigned" />        </id>        <property name="name" type="string">            <column name="NAME" not-null="true" />        </property>        <!-- idCard属性，IdCard类型，表达本类与IdCard的一对一关联 -->        <!-- 采用基于外键的一对一，本方无外键方 -->        <!-- property-ref属性：对方映射中外键类对应的属性名 -->        <one-to-one name="idCard" class="entity.IdCard" property-ref="person">         </one-to-one>    </class></hibernate-mapping>

然后看一下IdCard.hbm.xml文档

<?xml version="1.0" encoding="utf-8"?><!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN""http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd"><hibernate-mapping>    <class name="entity.IdCard" table="IdCard" schema="MYHR">        <id name="id">            <column name="ID"/>            <generator class="assigned" />        </id>        <property name="number">            <column name="NAME" not-null="true" />        </property>        <!-- person属性，Person类型，表示与Person类的一对一关联关系 -->        <!-- 采用基于外键的一对一关联方式，本方有外键 -->        <many-to-one name="person" column="personId" class="entity.Person" unique="true"></many-to-one>    </class></hibernate-mapping>

这样Person和IdCard之间的一对一关联关系就搭建好了，然后看一下测试类

package test;import static org.junit.Assert.*;import org.hibernate.Session;import org.hibernate.Transaction;import entity.IdCard;import entity.Person;import factory.HibernateSessionFactory;public class Test {private Session session = null;private Transaction tran = null;@org.junit.Testpublic void save() {session = HibernateSessionFactory.getSession();tran = session.beginTransaction();try{//新建对象Person p = new Person();p.setId(1);p.setName("张三");IdCard idCard = new IdCard();idCard.setId(1);idCard.setNumber("10001");p.setIdCard(idCard);idCard.setPerson(p);session.save(p);session.save(idCard);tran.commit();}catch(Exception e){tran.rollback();}}@org.junit.Testpublic void Get() {session = HibernateSessionFactory.getSession();tran = session.beginTransaction();try{Person person = (Person) session.get(Person.class, 1);IdCard idCard = person.getIdCard();System.out.println(person.getName()+"身份证号："+idCard.getNumber());tran.commit();}catch(Exception e){tran.rollback();}}//解除关系@org.junit.Testpublic void RemoveRelation() {session = HibernateSessionFactory.getSession();tran = session.beginTransaction();try{//从有外键方接触关联关系可以，不可以从无外键方解除IdCard idCard = (IdCard)session.get(IdCard.class, 1);idCard.setPerson(null);tran.commit();}catch(Exception e){tran.rollback();}}//删除@org.junit.Testpublic void DeleteRelation() {session = HibernateSessionFactory.getSession();tran = session.beginTransaction();try{//如果没有关联对方，可以直接删除。 //如果有关联对方，且可以维护关联关系，他就会先删除关联关系，在删除自己。//如果有关联关系，且不能维护关联关系，所以会执行删除自己，并且抛出异常。IdCard idCard = (IdCard)session.get(IdCard.class, 1);session.delete(idCard);tran.commit();}catch(Exception e){tran.rollback();}}}

这就是基于外键方式，基于主键的方式只需要在以上基础修改一下映射文件即可，下面分别看一下修改后的映射文件

首先看Person.hbm.xml

<?xml version="1.0" encoding="utf-8"?><!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN""http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd"><hibernate-mapping package="entity">    <class name="entity.Person" table="Person" schema="MYHR">        <id name="id" type="int">            <column name="ID" />            <generator class="assigned" />        </id>        <property name="name" type="string">            <column name="NAME" not-null="true" />        </property>        <!-- idCard属性，IdCard类型，表达本类与IdCard的一对一关联 -->        <!-- 采用基于主键的一对一，本方无外键方 -->        <one-to-one name="idCard" class="entity.IdCard"/>          </class></hibernate-mapping>

然后看IdCard.hbm.xml

<?xml version="1.0" encoding="utf-8"?><!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN""http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd"><hibernate-mapping package="entity"><class name="entity.IdCard" table="IdCard" schema="MYHR"><id name="id" type="int"><column name="ID" /><!-- 当使用基于主键的一对一映射时，有外键方的主键生成策略是foreign， --><!-- 参数property：生成主键值时所根据的对象 --><generator class="foreign">    <param name="property">person</param></generator></id><property name="number" type="string"><column name="NAME" not-null="true" /></property><!-- person属性，Person类型，表示与Person类的一对一关联关系 --><!-- 采用基于主键的一对一关联方式，本方有外键 --><one-to-one name="person" class="entity.Person"constrained="true" /></class></hibernate-mapping>