hibernate一对一双向外键关联
hibernate一对一双向外键关联
一、双向关联
在单向关联的基础上，另一个Object也持有关联对象
二、场景
一夫一妻
三、R
CREATE TABLE `wife` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`name` varchar(50) NOT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=15 DEFAULT CHARSET=utf8
CREATE TABLE `husband` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`name` varchar(50) NOT NULL,
`wifeid` int(11) DEFAULT NULL,
PRIMARY KEY (`id`),
KEY `fk_wife` (`wifeid`),
CONSTRAINT `fk_wife` FOREIGN KEY (`wifeid`) REFERENCES `wife` (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=20 DEFAULT CHARSET=utf8
四、O
wife
package com.linys.model;
/**
* Wife entity. @author MyEclipse Persistence Tools
*/
public class Wife implements java.io.Serializable {
// Fields
/**
*
*/
private static final long serialVersionUID = 1L;
private Integer id;
private String name;
private Husband husband;
// Constructors
/** default constructor */
public Wife() {
}
/** minimal constructor */
public Wife(String name) {
this.name = name;
}
// Property accessors
public Integer getId() {
return this.id;
}
public void setId(Integer id) {
this.id = id;
}
public String getName() {
return this.name;
}
public void setName(String name) {
this.name = name;
}
public Husband getHusband() {
return husband;
}
public void setHusband(Husband husband) {
this.husband = husband;
}
}
husband
package com.linys.model;
/**
* Husband entity. @author MyEclipse Persistence Tools
*/
public class Husband implements java.io.Serializable {
// Fields
/**
*
*/
private static final long serialVersionUID = 1L;
private Integer id;
private Wife wife;
private String name;
// Constructors
/** default constructor */
public Husband() {
}
/** minimal constructor */
public Husband(String name) {
this.name = name;
}
/** full constructor */
public Husband(Wife wife, String name) {
this.wife = wife;
this.name = name;
}
// Property accessors
public Integer getId() {
return this.id;
}
public void setId(Integer id) {
this.id = id;
}
public Wife getWife() {
return this.wife;
}
public void setWife(Wife wife) {
this.wife = wife;
}
public String getName() {
return this.name;
}
public void setName(String name) {
this.name = name;
}
}
五、映射文件
Wife.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">
<!--
Mapping file autogenerated by MyEclipse Persistence Tools
-->
<hibernate-mapping>
<class name="com.linys.model.Wife" table="wife">
<id name="id" type="java.lang.Integer">
<column name="id" />
<generator class="native" />
</id>
<property name="name" type="java.lang.String">
<column name="name" length="50" not-null="true" />
</property>
<one-to-one name="husband" class="com.linys.model.Husband" property-ref="wife" cascade="all"/>
</class>
</hibernate-mapping>
其中one-to-one是和单向外键关联不同地方
one-to-one:指定在Wife这个Object类中用于双向关联的属性husband
property-ref: 在关联对象中用于与此Object对象关联的属性
cascade: 级联
级联：
1 只有“关系标记”才有cascade属性：many-to-one，one-to-one ，any,
set(map, bag, idbag, list, array) + one-to-many(many-to-many)
2 级联指的是当主控方执行操作时，关联对象（被动方）是否同步执行同一操作。
pojo和它的关系属性的关系就是“主控方 -- 被动方”的关系，如果关系属性是一个set，那么被动方就是set中的一个一个元素，。
比如：学校（School）有三个属性：地区(Address),校长（TheMaster）和学生(Set， 元素为Student)
执行session.delete(school)时，级联决定是否执行session.delete(Address),session.delete(theMaster)，
是否对每个aStudent执行session.delete(aStudent)。
3 一个操作因级联cascade可能触发多个关联操作。前一个操作叫“主控操作”，后一个操作叫“关联操作”。
cascade属性的可选值：
all : 所有情况下均进行关联操作。
none：所有情况下均不进行关联操作。这是默认值。
save-update:在执行save/update/saveOrUpdate时进行关联操作。
delete：在执行delete时进行关联操作。
具体执行什么“关联操作”是根据“主控操作”来的：
“主控操作” “关联操作”
session.saveOrUpdate --> session.saveOrUpdate (执行saveOrUpdate实际上会执行save或者update)
session.save ----> session.saveOrUpdate
session.udpate --> session.saveOrUpdate
session.delete --> session.delete
4 主控操作和关联操作的先后顺序是“先保存one，再保存many；先删除many，再删除one；先update主控方，再update被动方”
对于one-to-one，当其属性constrained="false"（默认值）时，它可看作one-to-many关系；
当其属性constrained="true"时，它可看作many-to-one关系；
对many-to-many，它可看作one-to-many。
比如：学校（School）有三个属性：地区(Address),校长（TheMaster，其constrained="false"）和学生(Set， 元素为Student)
当执行session.save(school)时，
实际的执行顺序为：session.save(Address);
session.save(school);
session.save(theMaster);
for( 对每一个student ){
session.save(aStudent);
}
当执行session.delete(school)时，
实际的执行顺序为：session.delete(theMaster);
for( 对每一个student ){
session.delete(aStudent);
}
session.delete(school);
session.delete(Address);
当执行session.update(school)时，
实际的执行顺序为：session.update(school);
session.saveOrUpdate(Address);
session.saveOrUpdate(theMaster);
for( 对每一个student ){
session.saveOrUpdate(aStudent);
}
注意：update操作因级联引发的关联操作为saveOrUpdate操作，而不是update操作。
saveOrUpdate与update的区别是：前者根据操作对象是保存了还是没有保存，而决定执行update还是save
extends: 实际中，删除学校不会删除地区，即地区的cascade一般设为false
总结：级联（cascade）就是操作一个对象时，对它的属性（其cascade=true）也进行这个操作。一般将级联加在one一方,因为比如one方的记录改了，则在many中的关联记录也要跟着变化
Husband.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">
<!--
Mapping file autogenerated by MyEclipse Persistence Tools
-->
<hibernate-mapping>
<class name="com.linys.model.Husband" table="husband">
<id name="id" type="java.lang.Integer">
<column name="id" />
<generator class="native" />
</id>
<property name="name" type="java.lang.String">
<column name="name" length="50" not-null="true" />
</property>
<many-to-one name="wife" class="com.linys.model.Wife" unique="true">
<column name="wifeid" />
</many-to-one>
</class>
</hibernate-mapping>
六、测试类
package com.linys.model;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.cfg.Configuration;
import org.junit.AfterClass;
import org.junit.BeforeClass;
import org.junit.Test;
public class TestOne2OneUniFK {
static SessionFactory sf;
@BeforeClass
public static void setUpBeforeClass() throws Exception {
sf = new Configuration().configure().buildSessionFactory();
}
@Test
public void testOne2OneUniFK(){
Wife wife=new Wife();
wife.setName("wife");
Husband husband=new Husband();
husband.setName("husband");
husband.setWife(wife);
wife.setHusband(husband);
Session session=sf.openSession();
Transaction ts=session.beginTransaction();
//插入可以
// session.save(wife);
// session.save(husband);
//插入可以
// session.save(husband);
// session.save(wife);
//插入不行
// session.save(husband);
//插入可以,存wife的同时，存husband
session.save(wife);
ts.commit();
}
@AfterClass
public static void tearDownAfterClass() throws Exception {
sf.close();
}
}