关联是类（类的实例）之间的关系，表示有意义和值得关注的连接。
本系列将介绍Hibernate中主要的几种关联映射
Hibernate一对一主键单向关联
Hibernate一对一主键双向关联
Hibernate一对一外键单向关联
Hibernate一对一外键双向关联
Hibernate多对一单向关联
Hibernate多对一双向关联
Hibernate多对多关联
代码都写有注释，主要包括（核心配置文件，实体映射文件，实体类，测试类，数据库）主要操作有增删改查。
本篇主要介绍Hibernate一对一主键双向关联：
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>
<!-- 配置数据库连接驱动类 -->
<property name="connection.driver_class">com.mysql.jdbc.Driver</property>
<!-- 配置数据库连接字符串 -->
<property name="connection.url"><![CDATA[jdbc:mysql://localhost:3306/test1?useUnicode=true&characterEncoding=utf8]]></property>
<!-- 配置数据库连接用户名 -->
<property name="connection.username">root</property>
<!-- 配置数据库连接密码 -->
<property name="connection.password">123456</property>
<!-- 配置数据库方言 -->
<property name="dialect">org.hibernate.dialect.MySQLDialect</property>
<!-- 配置数据库表生成策略 -->
<!--<property name="hibernate.hbm2ddl.auto">update</property> -->
<!-- 配置是否打印显示SQL语句 -->
<property name="show_sql">true</property>
<!-- 配置是否格式化显示SQL语句 -->
<property name="format_sql">true</property>
<!-- 配置hibernate是否自动提交事务 -->
<!--<property name="hibernate.connection.autocommit">true</property> -->
<!-- 配置实体类对应的映射文件 -->
<!-- 一对一主键双向关联 -->
<mapping resource="com/great/entity2/People.hbm.xml"></mapping>
<mapping resource="com/great/entity2/IdCard.hbm.xml"></mapping>
</session-factory>
</hibernate-configuration>
People.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 package="com.great.entity2">
<!-- 配置实体类与数据库表的映射关系 -->
<class name="com.great.entity2.People" table="people">
<!-- 配置主键映射关系 -->
<id name="id" column="id" type="int">
<!-- 配置主键生成策略 -->
<generator class="foreign">
<param name="property">idCard</param>
</generator>
</id>
<!-- 配置属性和表字段映射关系 -->
<property name="pName" column="pName" type="string"></property>
<one-to-one name="idCard" class="com.great.entity2.IdCard"
cascade="all"></one-to-one>
</class>
</hibernate-mapping>
IdCard.hbm.xml
<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="com.great.entity2">
<class name="IdCard" table="idcard">
<id name="id" column="id" type="int">
<generator class="native">
</generator>
</id>
<!-- 配置属性和表字段映射关系 -->
<property name="cardCode" column="cardCode" type="string"></property>
<one-to-one class="com.great.entity2.People" name="people"
cascade="all"></one-to-one>
</class>
</hibernate-mapping>
People.java
package com.great.entity2;
public class People {
// 一对一主键关联
private int id;
private String pName;
private IdCard idCard;
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getpName() {
return pName;
}
public void setpName(String pName) {
this.pName = pName;
}
public IdCard getIdCard() {
return idCard;
}
public void setIdCard(IdCard idCard) {
this.idCard = idCard;
}
}
IdCard.java
package com.great.entity2;
public class IdCard {
private int id;
private String cardCode;
private People people;
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getCardCode() {
return CardCode;
}
public void setCardCode(String cardCode) {
CardCode = cardCode;
}
public People getPeople() {
return people;
}
public void setPeople(People people) {
this.people = people;
}
}
TestOneToOneUniqueBoth.java(测试类)
package com.great.test;
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;
import com.great.entity2.IdCard;
import com.great.entity2.People;
public class TestOneToOneUniqueBoth {
static Session session;
// 一对一主键双向关联
@BeforeClass
public static void setUpBeforeClass() throws Exception {
// 加载hibernate主配置文件
Configuration cfg = new Configuration().configure();
// 构建session工厂
SessionFactory sf = cfg.buildSessionFactory();
// 打开session
session = sf.openSession();
}
@AfterClass
public static void tearDownAfterClass() throws Exception {
// 关闭session，释放资源
session.close();
}
// select1,通过people查询idcard
@Test
public void testOneToOneSelect1() {
People people = (People) session.get(People.class, 1);
System.out.println("身份证号码：" + people.getIdCard().getCardCode());
System.out.println("姓名：" + people.getpName());
}
// select2, 通过idcard查询people
@Test
public void testOneToOneSelect2() {
IdCard idCard = (IdCard) session.get(IdCard.class, 1);
System.out.println("身份证号码：" + idCard.getCardCode());
System.out.println("姓名：" + idCard.getPeople().getpName());
}
// insert1, 通过people插入数据 ,两条insert,【先insert idCard,后insert
// people,涉及键的问题，必须顺序的保存数据,而insert语句就是按顺序的，和select,delete,update不一样】
@Test
public void testOneToOneSave1() {
Transaction ts = session.beginTransaction();
// 设置idcard
IdCard idCard = new IdCard();
idCard.setCardCode("411487199505051234");
// 设置people
People people = new People();
people.setpName("王胖");
// 互相保存
idCard.setPeople(people);
people.setIdCard(idCard);
// 保存idcard,必须保存idCard,保存People出错，Hibernate这次首先持久化了people对象
// 由于people表中的id字段建立了外键关系，故持久化失败.
session.save(idCard);
ts.commit();
}
/*
* delete1 通过删除idCard删除数据，一条select,两条delete,先delete people,再delete idCard
* ,【涉及键的问题，与select有关，所以只能有一种delete的方法】
*/
@Test
public void testOneToOneDelete1() {
Transaction ts = session.beginTransaction();
IdCard idCard = (IdCard) session.get(IdCard.class, 10);
session.delete(idCard);
ts.commit();
}
// delete2 通过删除idCard删除数据，
// @Test
// public void testOneToOneDelete2() {
// Transaction ts = session.beginTransaction();
// People people = (People) session.get(People.class, 8);
// session.delete(people);
// ts.commit();
// }
/*
* update1 ，通过idCard更新数据,发出一条select,两条update ,先update people,再update inCard
* 【因为要想update idCard,就得update people,不涉及键的问题，只与select有关】
*/
@Test
public void testOneToOneUpdate1() {
Transaction ts = session.beginTransaction();
IdCard idCard = (IdCard) session.get(IdCard.class, 8);
idCard.setCardCode("123456789");
idCard.getPeople().setpName("张起灵aaa");
session.update(idCard);
ts.commit();
}
/*
* update2 ，通过people更新数据,发出一条select,两条update ,先update idCard,再update
* people【因为要想update people,就得update idCard,不涉及键的问题，只与select有关】
*/
@Test
public void testOneToOneUpdate2() {
Transaction ts = session.beginTransaction();
People people = (People) session.get(People.class, 8);
people.setpName("小哥");
people.getIdCard().setCardCode("66666");
session.update(people);
ts.commit();
}
}
数据库：
people表
两个字段id pName
idcard表
两个字段id cardCode
注意：在people表上建立外键关系。