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

     
         
            
               
       
        com.mysql.jdbc.Driver
               
               
       
               
               
       
        root
               
               
       
        123456
               
               
       
        org.hibernate.dialect.MySQLDialect
               
               
               
               
       
        true
               
               
       
        true
               
               
               
               
               
               
           
      
     

People.hbm.xml

     
         
          
              
               
                   
                    
                        
         idCard            
                
               
               
               
           
      
     

IdCard.hbm.xml

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。