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.Test
public 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.Test
public 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.Test
public 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.Test
public 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>