Hibernate复习(6)-单向一对一外键关联映射

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。

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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 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 name="code"><?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`);

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?? citizen表

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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`);

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Hibernate辅助类

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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

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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;@BeforeClasspublic static void init(){sessionFactory = HibernateUtil.getSessionFactory();}@AfterClasspublic static void destroy(){sessionFactory = null;}@Testpublic 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();}@Testpublic 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());}}

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