MyBitis(iBitis)系列随笔之五：多表(一对多关联查询)

 

         这篇博文介绍的是多表中的一对多表关联查询
还是按照上一篇的步骤，先做一些准备工作；创建两张表：一张是用户，一张是用户所对应的移动手机，一户用户可以有部移动手机。
      这是用户t_user表

              
        这是移动电话t_mobile表
              
           在Java实体对象对中，一对多可以根据List和Set来实现，两者在mybitis中都是通过collection标签来配合使用，稍后会做详细配置介绍

          创建表对应的JavaBean对象

Mobile  Bean

public class Mobile {
    private int id;
    private String telnumber;

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getTelnumber() {
        return telnumber;
    }

    public void setTelnumber(String telnumber) {
        this.telnumber = telnumber;
    }

}

User Bean

package com.jefry;

import java.util.List;

public class User {
    private int id;
    private String userName;
    private String password;
          private List<Mobile> mobiles; //这里也可以是Set集合

    public List<Mobile> getMobiles() {
        return mobiles;
    }

    public void setMobiles(List<Mobile> mobiles) {
        this.mobiles = mobiles;
    }

    public String getUserName() {
        return userName;
    }

    public void setUserName(String userName) {
        this.userName = userName;
    }

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

}

 

在上一篇的基础上改写映射文件：

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="user">
     <resultMap id="userResultMap" type="User">
        <id property="id" column="id" javaType="int" jdbcType="INTEGER" />
        <result property="userName" column="name" javaType="string" jdbcType="VARCHAR"/>
        <result property="password" column="pass" javaType="string" jdbcType="VARCHAR"/>
        <collection property="mobiles" column="userid" ofType="Mobile">
            <id property="id" column="id" javaType="int" jdbcType="INTEGER"/>
            <result property="telnumber" column="telnumber" javaType="string" jdbcType="VARCHAR"/>
        </collection>
     </resultMap>

    <!--多表查询操作-->
    <select id="selectUser" parameterType="int"  resultMap="userResultMap" >
        <!--分别为mobile的主键id与user的主键id赋值别名,避免因为两个表字段名称相同而注入到对应对象名称冲突-->
        select m.id m_id,m.telnumber,u.id u_id,u.name,u.pass from t_mobile m,t_user u where m.userid = u.id and u.id = #{id}
    </select>
</mapper>

 

最后，通过测试OK

 

public class Test {
    static String resource = "mybatis-config.xml";

    public static void main(String[] args) throws IOException {
        InputStream inputStream = Resources.getResourceAsStream(resource);
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        SqlSession session = sqlSessionFactory.openSession();
        try {
            User user = session.selectOne("user.selectUser", 1);
            List<Mobile> mobiles = user.getMobiles();
            for(Mobile mobile : mobiles) {
                System.out.println("user:" + user.getUserName() + ",tel:" + mobile.getTelnumber());
            }


        } finally {
            session.close();
        }
    }

}