Hibernate 双向一对一关联

本文只介绍实际开发中常用的设计模式（双向一对一关联）

其原理只是多对一的一种特例，只需增加一个unique="true"

下面看代码：

2个实体测试类：Man和Woman；理解为（一个男人可以娶一个女人，一个女人嫁一个男人）

package ray.one2one;

public class Man {
private int id;
private String name;
private Woman woman;
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public Woman getWoman() {
return woman;
}
public void setWoman(Woman woman) {
this.woman = woman;
}
}

Woman类：

package ray.one2one;

public class Woman {
private int id;
private String name;
private Man man;
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public Man getMan() {
return man;
}
public void setMan(Man man) {
this.man = man;
}

}

要点：Man和Woman各自维护一个引用对象，互相指向一个对象

再看配置文件：

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">

<hibernate-mapping package="ray.one2one">
<class name="Man" table="_man" lazy="true">
<id name="id">
<generator class="native"></generator>
</id>
<property name="name"></property>
<!-- 双向一对一关联, property-ref指明在关联类必须有Man类的man属性的get和set -->
<!-- 单向一对一则不需要此属性 -->
<one-to-one name="woman" class="Woman" property-ref="man"
cascade="all"></one-to-one>
</class>
</hibernate-mapping>

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">

<hibernate-mapping package="ray.one2one">
<class name="Woman" table="_woman" lazy="true">
<id name="id">
<generator class="native"></generator>
</id>
<property name="name"></property>
<!-- 双向一对一外键关联-->
<many-to-one name="man" unique="true" column="m_id"
cascade="all"></many-to-one>
</class>
</hibernate-mapping>

最后看下测试类代码：

package ray.one2one;

import org.hibernate.Session;
import ray.SessionUtil.HibernateSessionFactory;

public class Test {
public static void main(String[] args) {
Woman woman = new Woman();
woman.setName("文苹");
Man man = new Man();
man.setName("雷盼");
man.setWoman(woman);
woman.setMan(man);
Session session = HibernateSessionFactory.getSession();
session.beginTransaction();

session.save(woman);
session.getTransaction().commit();
session.close();
}
}

输出结果：

Hibernate:
alter table _woman
add index FK_gxnyefreb964vdnbshbbmreou (m_id),
add constraint FK_gxnyefreb964vdnbshbbmreou
foreign key (m_id)
references _man (id)

Hibernate: 
    insert 
    into
        _man
        (name) 
    values
        (?)
Hibernate: 
    insert 
    into
        _woman
        (name, m_id) 
    values
        (?, ?)