Hibernate之映射一对一关联

2022-11-16 11:32:46

一.一对一关联的概念：

一对一之间的关联是指：两张表中的信息是一对一的关系，比如我们每个人和身份证的关系，一个人对应一张身份证，一张身份证也只能对应一个人。

Hibernate提供了两种映射一对一关联关系的方式：按照外键映射和按照主键映射。

在下面的例子中我们分别以两张表：员工表和员工档案表为例：介绍这两种映射关系方式。

二.按外键映射

1.关联的外键可存放于任意一端，并在存放外键的一端增加<many-to-one>元素，能够增加唯一约束实现一对一关联。
2.<many-to-one>元素的unique="true"属性，表示1-1关联；name属性指定关联属性的属性名
3.另一端需要使用<one-to-one>元素，在元素中使用"property-ref"属性（可不加），指定使用被关联实体主键以外的字段作为关联字段。

I.首先建立两张表的实体类：

Users1:

package cn.entity;
/**
 * 员工账号实体类
 * @author hyj
 *
 */
public class Users1 {
    private Integer userid;//员工账号
    private String username;//员工名称
    private String userpass;//员工密码
    private Resume1 resume1;//员工的档案
    public Users1() {
        super();
        // TODO Auto-generated constructor stub
    }

    public Users1(String username, String userpass) {
        super();
        this.username = username;
        this.userpass = userpass;
    }

    public Users1(Integer userid, String username, String userpass,
            Resume1 resume1) {
        super();
        this.userid = userid;
        this.username = username;
        this.userpass = userpass;
        this.resume1 = resume1;
    }
    public Integer getUserid() {
        return userid;
    }
    public void setUserid(Integer userid) {
        this.userid = userid;
    }
    public String getUsername() {
        return username;
    }
    public void setUsername(String username) {
        this.username = username;
    }
    public String getUserpass() {
        return userpass;
    }
    public void setUserpass(String userpass) {
        this.userpass = userpass;
    }
    public Resume1 getResume1() {
        return resume1;
    }
    public void setResume1(Resume1 resume1) {
        this.resume1 = resume1;
    }

}

Resume1:

package cn.entity;
/**
 * 员工档案实体类
 * @author hyj
 *
 */
public class Resume1 {
    private Integer resid;
    private String resname;//档案名称
    private String rescardno;//档案编号
    private Users1 users1;//所属员工
    public Resume1() {
        super();
        // TODO Auto-generated constructor stub
    }
    public Resume1(Integer resid, String resname, String rescardno,
            Users1 users1) {
        super();
        this.resid = resid;
        this.resname = resname;
        this.rescardno = rescardno;
        this.users1 = users1;
    }

    public Resume1(String resname, String rescardno) {
        super();
        this.resname = resname;
        this.rescardno = rescardno;
    }
    public Integer getResid() {
        return resid;
    }
    public void setResid(Integer resid) {
        this.resid = resid;
    }
    public String getResname() {
        return resname;
    }
    public void setResname(String resname) {
        this.resname = resname;
    }
    public String getRescardno() {
        return rescardno;
    }
    public void setRescardno(String rescardno) {
        this.rescardno = rescardno;
    }
    public Users1 getUsers1() {
        return users1;
    }
    public void setUsers1(Users1 users1) {
        this.users1 = users1;
    }

}

II.建立两个实体类的映射文件：

Resume1.hbm.xml：

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
        "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
        "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
       <hibernate-mapping package="cn.entity">
       <class name="Resume1" table="Resume1">
          <id name="resid" column="resid">
            <generator class="native"></generator>
          </id>
       <property name="resname" column="resname" type="string"></property>
     <property name="rescardno" column="rescardno" type="string"></property>
    <many-to-one name="users1" class="Users1" column="RESUSERID" cascade="all" unique="true"></many-to-one>
       </class>
       </hibernate-mapping>

Users1.hbm.xml：

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
        "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
        "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
       <hibernate-mapping package="cn.entity">
       <class name="Users1" table="Users1">
          <id name="userid" column="USERID">
            <generator class="native"></generator>
          </id>
       <property name="username" column="username" type="string"></property>
     <property name="userpass" column="userpass" type="string"></property>
     <one-to-one name="resume1" class="Resume1" property-ref="users1"></one-to-one>
       </class>
       </hibernate-mapping>

III：建立测试类：

package cn.test;

import org.hibernate.Session;
import org.hibernate.Transaction;
import org.junit.Test;

import cn.entity.Resume1;
import cn.entity.Users1;
import cn.util.HibernateUtil;

public class HappyTest {
    /**
     * 添加信息
     */
     @Test
     public void addInfoTest(){
          //1.获取session对象
         Session session=HibernateUtil.currentSession();
         //2.开启事务
         Transaction tx = session.beginTransaction();
         //3.准备一个用户对象
         Users1 users1=new Users1("hyj","123");
         //4.创建一个档案对象
         Resume1 resume1=new Resume1("高级机密档案","hyj0819");
         //5.让用户归属档案，档案归属用户
         users1.setResume1(resume1);
         resume1.setUsers1(users1);
         //6.session.save保存档案即可，应为cascade的属性值为all，保存档案的同时自动保存用户
         session.save(resume1);
         //7.提交事务
         tx.commit();
         //8.关闭session
         HibernateUtil.closeSession();
         System.out.println("添加成功");
     }

     /**
      * 查询员工档案的时候同时加载用户信息
      */
      @Test
      public void selectInfoTest(){
           //1.获取session对象
          Session session=HibernateUtil.currentSession();
          //2.获取员工档案对象
          Resume1 resume1=(Resume1)session.load(Resume1.class, 1);
            //3.根据员工档案获取用户的信息
           Users1 users1= resume1.getUsers1();
          //4.输出结果
           System.out.println("档案名称："+resume1.getResname());
           System.out.println("用户姓名："+users1.getUsername());
          //8.关闭session
          HibernateUtil.closeSession();
      }

}

user1表：

resume1表：

三.按主键映射

1.关联要求两个对象的主键必须保持一致，通过两个表的主键建立关联关系须外键参与。
2.基于主键的映射策略：指一端的主键生成器使用"class="foreign""策略，表明根据"对方"的主键来生成自己的主键，自己并不能独立生成主键。<param>子元素指定使用当前持久化类的哪个属性作为"对方"。
3.采用foreign主键生成器策略的一端增加<one-to-one>元素映射关联属性，并在<one-to-one>元素中增加constrained="true"属性；另一端也增加<one-to-one>元素映射关联属性。
4."constrained="true""属性：指定当前持久化类对应的数据库表的主键添加一个外键约束，引用被关联的对象（"对方"）所对应的数据库表主键

I.首先建立两张表的实体类：

为了区分案例此表为Users2 Resume2:

Users2:

package cn.entity;
/**
 * 员工账号实体类
 * @author hyj
 *
 */
public class Users2 {
    private Integer userid;
    private String username;
    private String userpass;
    private Resume2 resume2;
    public Users2() {
        super();
        // TODO Auto-generated constructor stub
    }
    public Users2(Integer userid, String username, String userpass,
            Resume2 resume2) {
        super();
        this.userid = userid;
        this.username = username;
        this.userpass = userpass;
        this.resume2 = resume2;
    }
    public Integer getUserid() {
        return userid;
    }
    public void setUserid(Integer userid) {
        this.userid = userid;
    }
    public String getUsername() {
        return username;
    }
    public void setUsername(String username) {
        this.username = username;
    }
    public String getUserpass() {
        return userpass;
    }
    public void setUserpass(String userpass) {
        this.userpass = userpass;
    }
    public Resume2 getResume2() {
        return resume2;
    }
    public void setResume2(Resume2 resume2) {
        this.resume2 = resume2;
    }
    public Users2(String username, String userpass) {
        super();
        this.username = username;
        this.userpass = userpass;
    }

}

Resume2:

package cn.entity;
/**
 * 员工档案实体类
 * @author hyj
 *
 */
public class Resume2 {
    private Integer resid;
    private String resname;
    private String rescardno;
    private Users2 users2;
    public Resume2() {
        super();
        // TODO Auto-generated constructor stub
    }
    public Resume2(Integer resid, String resname, String rescardno,
            Users2 users2) {
        super();
        this.resid = resid;
        this.resname = resname;
        this.rescardno = rescardno;
        this.users2 = users2;
    }
    public Resume2(String resname, String rescardno) {
        super();
        this.resname = resname;
        this.rescardno = rescardno;
    }
    public Integer getResid() {
        return resid;
    }
    public void setResid(Integer resid) {
        this.resid = resid;
    }
    public String getResname() {
        return resname;
    }
    public void setResname(String resname) {
        this.resname = resname;
    }
    public String getRescardno() {
        return rescardno;
    }
    public void setRescardno(String rescardno) {
        this.rescardno = rescardno;
    }
    public Users2 getUsers2() {
        return users2;
    }
    public void setUsers2(Users2 users2) {
        this.users2 = users2;
    }

}

II.建立两个实体类的映射文件：

Resume2.hbm.xml:

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
        "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
        "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
       <hibernate-mapping package="cn.entity">
       <class name="Resume2" table="Resume2">
          <id name="resid" column="resid">
            <generator class="native"></generator>
          </id>
       <property name="resname" column="resname" type="string"></property>
     <property name="rescardno" column="rescardno" type="string"></property>
    <one-to-one  name="users2" cascade="all" class="Users2"/>
       </class>

       </hibernate-mapping>

Users2.hbm.xml:

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
        "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
        "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
       <hibernate-mapping package="cn.entity">
       <class name="Users2" table="Users2">
          <id name="userid" column="USERID" >
        <generator class="foreign">
          <param name="property">resume2</param>
        </generator>
          </id>
       <property name="username" column="username" type="string"></property>
     <property name="userpass" column="userpass" type="string"></property>
     <one-to-one name="resume2" class="Resume2" constrained="true"></one-to-one>
       </class>

       </hibernate-mapping>

III.建立测试类：

package cn.test;

import org.hibernate.Session;
import org.hibernate.Transaction;
import org.junit.Test;

import cn.entity.Resume2;
import cn.entity.Users2;
import cn.util.HibernateUtil;

public class HappyTest {
    /**
     * 添加信息
     */
     @Test
     public void addInfoTest(){
          //1.获取session对象
         Session session=HibernateUtil.currentSession();
         //2.开启事务
         Transaction tx = session.beginTransaction();
         //3.准备一个用户对象
         Users2 users2=new Users2("hyj","123");
         //4.创建一个档案对象
         Resume2 resume2=new Resume2("高级机密档案","hyj0819");
         //5.让用户归属档案，档案归属用户
         users2.setResume2(resume2);
         resume2.setUsers2(users2);
         //6.session.save保存档案即可，应为cascade的属性值为all，保存档案的同时自动保存用户
         session.save(resume2);
         //7.提交事务
         tx.commit();
         //8.关闭session
         HibernateUtil.closeSession();
         System.out.println("添加成功");
     }

     /**
      * 查询员工档案的时候同时加载用户信息
      */
      @Test
      public void selectInfoTest(){
           //1.获取session对象
          Session session=HibernateUtil.currentSession();
          //2.获取员工档案对象
          Resume2 resume2=(Resume2)session.load(Resume2.class, 3);
            //3.根据员工档案获取用户的信息
           Users2 users2= resume2.getUsers2();
          //4.输出结果
           System.out.println("档案名称："+resume2.getResname());
           System.out.println("用户姓名："+users2.getUsername());
          //8.关闭session
          HibernateUtil.closeSession();
      }

}

users2表

resume2表

码农公寓

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