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一对一外键单向关联：
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 -->
<!-- 一对一单向外键关联 -->
<mapping resource="com/great/entity4/People.hbm.xml"></mapping>
<mapping resource="com/great/entity4/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.entity4">
<!-- 配置实体类与数据库表的映射关系 -->
<class name="People" table="people1">
<!-- 配置主键映射关系 -->
<id name="id" column="id" type="int">
<!-- 配置主键生成策略 这个主键生成策略并没有什么影响 -->
<generator class="native">
</generator>
</id>
<!-- 配置属性和表字段映射关系 一对一外键单向关联 -->
<property name="pName" column="pName" type="string"></property>
<many-to-one name="idCard" unique="true" cascade="all">
<column name="card_id"></column>
</many-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.entity4">
<class name="IdCard" table="idcard1">
<id name="card_id" column="id" type="int">
<generator class="identity">
</generator>
</id>
<!-- 配置属性和表字段映射关系 一对一外键单向关联 -->
<property name="cardCode" column="cardCode" type="string"></property>
</class>
</hibernate-mapping>
People.java
package com.great.entity4;
public class People {
// 一对一外键单向关联
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.entity4;
public class IdCard {
// 一对一外键单向关联
private int card_id;
private String cardCode;
public int getCard_id() {
return card_id;
}
public void setCard_id(int card_id) {
this.card_id = card_id;
}
public String getCardCode() {
return CardCode;
}
public void setCardCode(String cardCode) {
CardCode = cardCode;
}
}
TestOneToOneForeignUn.java(测试类)
package com.great.test;
import org.hibernate.Transaction;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;
import org.junit.AfterClass;
import org.junit.BeforeClass;
import org.junit.Test;
import com.great.entity4.IdCard;
import com.great.entity4.People;
public class TestOneToOneForeignUnidirectional {
static Session session;
// 一对一外键单向关联，所以真正意义上的增删改查都是通过外键的一方进行操作的，否则将没有失去了关联的意义
@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();
}
// 只能通过people进行查询
@Test
public void testOneToOneSelect1() {
People people1 = (People) session.get(People.class, 1);
System.out.println("身份证号码：" + people1.getIdCard().getCardCode());
System.out.println("姓名是：" + people1.getpName());
}
// insert数据,只能通过保存people来插入数据
@Test
public void testOneToOneSave1() {
Transaction ts = session.beginTransaction();
IdCard idCard = new IdCard();
idCard.setCardCode("4567891234566");
People people = new People();
people.setpName("张起灵");
people.setIdCard(idCard);
session.save(people);
ts.commit();
}
// delete数据，只能通过people删除了,级联删除inCard。
@Test
public void testOneToOneDelete1() {
Transaction ts = session.beginTransaction();
People people = (People) session.get(People.class, 5);
session.delete(people);
ts.commit();
}
// 更新数据1，通过改变people进行数据更新，不能通过改变idCard进行数据更新
@Test
public void testOneToOneUpdate1() {
Transaction ts = session.beginTransaction();
People people = (People) session.get(People.class, 5);
people.setpName("张起灵1");
people.getIdCard().setCardCode("511381199612120254");
/*
* session.update(people);
* update和saveOrUpdate的区别在于后者在数据库中不存在此对象的情况下插入，所以效率低。
*/
session.saveOrUpdate(people);
ts.commit();
}
// 更新数据2，两方都更新，但是没必要，如果这样就失去了关联的意思并且增加了复杂度。
@Test
public void testOneToOneUpdate2() {
Transaction ts = session.beginTransaction();
People people = (People) session.get(People.class, 5);
IdCard idCard = (IdCard) session.get(IdCard.class, 5);
people.setpName("小哥");
idCard.setCardCode("311381199612120254");
session.update(people);
session.update(idCard);
ts.commit();
}
}
数据库：
people1表
三个字段id pName card_id(外键)
idcard1表
两个字段id cardCode
注意：在people表的card_id上建立外键关系。