Hibernate温习(6)--单向一对一外键关联映射

hibernate一对一唯一外键关联映射（单向关联Citizen---->IDCard）

一对唯一外键关联映射是多对一关联映射的特例

 基于外键关联的单向一对一关联和单向多对一关联几乎是一样的。唯一的不同就是单向一对一关联中的外键字段具有唯一性约束。只需要将原来的many-to-one元素增加unique="true"属性，用于表示N的一端也必须是唯一的，在N的一端增加了唯一的约束，即成为单向1-1。

 

具体做法

1. 单向一对一关联：对象模型和关系模型不匹配。

   对象模型上：主控方持有被控方实体类的引用。

   关系模型上：主控方对应表中添加一个外键引用自被控方的主键，这个外键必须添加唯一约束。

2. 在主控方的映射文件中：

  <many-to-one name="属性名" column="外键名" unique="true" [cascade="all"]/>

Citizen.java

package com.javacrazyer.domain;

public class Citizen {
	private Long id;
	private String name;
	private Boolean gender;
	
	//一对一关联中：主控方持有被控方的引用
	private IDCard idCard;

	public Long getId() {
		return id;
	}

	public void setId(Long id) {
		this.id = id;
	}

	public String getName() {
		return name;
	}

	public void setName(String name) {
		this.name = name;
	}

	public Boolean getGender() {
		return gender;
	}

	public void setGender(Boolean gender) {
		this.gender = gender;
	}

	public IDCard getIdCard() {
		return idCard;
	}

	public void setIdCard(IDCard idCard) {
		this.idCard = idCard;
	}
	
	public String toString(){
		return "id=" + this.id + ",name=" + this.name + ",gender=" + this.gender;
	}
}

 IDCard.java

package com.javacrazyer.domain;

public class IDCard {
	private Long id;
	private String no;
	public Long getId() {
		return id;
	}
	public void setId(Long id) {
		this.id = id;
	}
	public String getNo() {
		return no;
	}
	public void setNo(String no) {
		this.no = no;
	}
	
	public String toString(){
		return "id=" + id + ",no=" + this.no;
	}
}

 Citizen.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.javacrazyer.domain.Citizen">
		<id name="id" column="id">
            <generator class="native"/>
        </id>
        <property name="name"/>
        <property name="gender"/>
		
		<!-- 映射基于外键一对一关联 -->
		<many-to-one name="idCard" column="card_id" unique="true" cascade="all"/>
	</class>
</hibernate-mapping>

 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.javacrazyer.domain.IDCard" >
		<id name="id" column="id">
            <generator class="native"/>
        </id>
        <property name="no"/>
	</class>
</hibernate-mapping>

 hibernate.cfg.xml

<?xml version="1.0" encoding="utf-8" ?>
<!DOCTYPE hibernate-configuration PUBLIC
	"-//Hibernate/Hibernate Configuration DTD 3.0//EN"
	"http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">
<hibernate-configuration>
	<session-factory>
		<!-- 数据库连接参数配置 -->
		<property name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property>
		<property name="hibernate.connection.url">jdbc:mysql:///test</property>
		<property name="hibernate.connection.username">root</property>
		<property name="hibernate.connection.password">root</property>
		<!-- 数据库言的配置 -->
		<property name="hibernate.dialect">org.hibernate.dialect.MySQLDialect</property>
		<property name="hibernate.show_sql">true</property>
		<property name="hibernate.format_sql">true</property>
		<property name="hibernate.hbm2ddl.auto">update</property>
		<!-- 声明实体关系映射文件 -->
		<mapping resource="com/javacrazyer/domain/IDCard.hbm.xml" />
		<mapping resource="com/javacrazyer/domain/Citizen.hbm.xml" />
	</session-factory>
</hibernate-configuration>

 启动下Hibernate，自动生成数据库表，数据库表的DDL语句如下

   idcard表

   create table `test`.`idcard`(
        `id` BIGINT not null auto_increment,
       `no` VARCHAR(255),
        primary key (`id`)
    );

    create unique index `PRIMARY` on `test`.`idcard`(`id`);

 

   citizen表

 

create table `test`.`citizen`(
        `id` BIGINT not null auto_increment,
       `name` VARCHAR(255),
       `gender` BIT,
       `card_id` BIGINT unique,
        primary key (`id`)
    );

    alter table `test`.`citizen`  
        add index `FK92029348E9FA33E0`(`card_id`), 
        add constraint `FK92029348E9FA33E0` 
        foreign key (`card_id`) 
        references `test`.`idcard`(`id`);
    create unique index `PRIMARY` on `test`.`citizen`(`id`);
    create unique index `card_id` on `test`.`citizen`(`card_id`);
    create index `FK92029348E9FA33E0` on `test`.`citizen`(`card_id`);

 

 

   

Hibernate辅助类

 

package com.javacrazyer.common;

import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;

/**
 * Hibernate工具类
 * 
 */
public class HibernateUtil {
	private static final SessionFactory factory;
	
	private HibernateUtil(){}
	
	static{
		//加载Hibernate全局配置文件,根据配置信息创建SessionFactory工厂实例
		factory = new Configuration().configure().buildSessionFactory();
	}
	
	public static SessionFactory getSessionFactory(){
		return factory;
	}
}

 测试类

 

package com.javacrazyer.test;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.junit.AfterClass;
import org.junit.BeforeClass;
import org.junit.Test;

import com.javacrazyer.common.HibernateUtil;
import com.javacrazyer.domain.Citizen;
import com.javacrazyer.domain.IDCard;

public class MappingTest {
	private static SessionFactory sessionFactory;
	
	@BeforeClass
	public static void init(){
		sessionFactory = HibernateUtil.getSessionFactory();
	}
	
	@AfterClass
	public static void destroy(){
		sessionFactory = null;
	}
	
	@Test
	public void testSave(){
		Session session = sessionFactory.openSession();
		session.beginTransaction();
		
		IDCard ic = new IDCard();
		ic.setNo("xx0001");
		
		Citizen citizen = new Citizen();
		citizen.setName("赵C");
		
		//设置一对一的关联
		citizen.setIdCard(ic);
		
		session.save(citizen);
		
		session.getTransaction().commit();
		session.close();
	}
	
	@Test
	public void testGet(){
		Session session = sessionFactory.openSession();
		session.beginTransaction();
		
		Citizen c = (Citizen)session.get(Citizen.class, Long.valueOf(1));
		
		System.out.println(c.getName());
		
		IDCard idcard = c.getIdCard();
		
		System.out.println(idcard.getId());
		
		session.getTransaction().commit();
		session.close();
		
		System.out.println(idcard.getNo());
	}
	
}