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一对一外键双向关联：
hibernate.cfg.xml
com.mysql.jdbc.Driver root 123456 org.hibernate.dialect.MySQLDialect true true
People.hbm.xml
IdCard.hbm.xml
People.java
package com.great.entity5;public class People { // 一对一外键双向关联 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.entity5;public class IdCard { // 一对一外键双向关联 private int card_id; private String cardCode; private People people; 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; } public People getPeople() { return people; } public void setPeople(People people) { this.people = people; }} TestOneToOneForeignBoth.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.entity5.IdCard;import com.great.entity5.People;public class TestOneToOneForeignBoth { static Session session; // 一对一外键双向关联 @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 @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("姓名是：" + people.getpName()); } // select2,通过idCard @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("姓名是：" + idCard.getPeople().getpName()); } // insert1数据,通过保存people来插入数据 @Test public void testOneToOneSave1() { Transaction ts = session.beginTransaction(); IdCard idCard = new IdCard(); idCard.setCardCode("124567891234566"); People people = new People(); people.setpName("张起灵2"); idCard.setPeople(people);// 可加可不加 people.setIdCard(idCard); session.save(people); ts.commit(); } // insert2数据,通过保存inCard来插入数据 @Test public void testOneToOneSave2() { Transaction ts = session.beginTransaction(); IdCard idCard = new IdCard(); idCard.setCardCode("124567891234566"); People people = new People(); people.setpName("张起灵2"); people.setIdCard(idCard);// 必须加，否则失败 idCard.setPeople(people); session.save(idCard); ts.commit(); } // delete1数据，删除people,级联删除inCard。发出两条查询两条删除语句 @Test public void testOneToOneDelete1() { Transaction ts = session.beginTransaction(); People people = (People) session.get(People.class, 12); session.delete(people); ts.commit(); } /* * delete2数据，通过删除idCard，级联删除people. * delete数据。发出两条查询两条删除语句，也是先删除people再删除idCard */ @Test public void testOneToOneDelete2() { Transaction ts = session.beginTransaction(); IdCard idCard = (IdCard) session.get(IdCard.class, 14); session.delete(idCard); ts.commit(); } // 更新数据1，通过people进行更新 @Test public void testOneToOneUpdate1() { Transaction ts = session.beginTransaction(); People people = (People) session.get(People.class, 11); 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，通过idCard进行更新 @Test public void testOneToOneUpdate2() { Transaction ts = session.beginTransaction(); IdCard idCard = (IdCard) session.get(IdCard.class, 8); idCard.getPeople().setpName("张起灵3"); idCard.setCardCode("311381199612120254"); 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。