SSM15.2【Mybatis：Mybatis的多表操作之一对多】

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

package com.haifei.domain;

import java.util.Date;
import java.util.List;

/**
 * user表
 */
public class User {

    private int id;
    private String username;
    private String password;
    private Date birthday;

    //描述的是当前用户存在哪些订单
    private List<Order> orderList;
    public List<Order> getOrderList() {
        return orderList;
    }
    public void setOrderList(List<Order> orderList) {
        this.orderList = orderList;
    }


    public Date getBirthday() {
        return birthday;
    }

    public void setBirthday(Date birthday) {
        this.birthday = birthday;
    }

    public int getId() {
        return id;
    }

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

    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;
    }

   
    //1:n
    @Override
    public String toString() {
        return "User{" +
                "id=" + id +
                ", username='" + username + '\'' +
                ", password='" + password + '\'' +
                ", birthday=" + birthday +
                ", orderList=" + orderList +
                '}';
    }
    
}

package com.haifei.mapper;

import com.haifei.domain.User;

import java.util.List;

public interface UserMapper {

    public List<User> findAll();

}

<?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="com.haifei.mapper.UserMapper">

    <resultMap id="userMap" type="user">
        <!--user的信息-->
        <id column="uid" property="id"/>
        <result column="username" property="username"/>
        <result column="password" property="password"/>
        <result column="birthday" property="birthday"/>
        <!--user内部的orderList信息-->
        <collection property="orderList" ofType="order">
            <!--配置集合信息,property:集合名称,ofType：当前集合中的数据类型-->
            <!--封装order的数据-->
            <id column="oid" property="id"/>
            <result column="ordertime" property="ordertime"/>
            <result column="total" property="total"/>
        </collection>
    </resultMap>

    <select id="findAll" resultMap="userMap">
        SELECT *,o.id oid FROM user u,orders o WHERE u.id=o.uid
    </select>

   
</mapper>

/**
     * 一对多查询
     *  场景：一个用户有多个订单
     * @throws IOException
     */
    @Test
    public void test2() throws IOException {
        InputStream resourceAsStream = Resources.getResourceAsStream("sqlMapConfig.xml");
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(resourceAsStream);
        SqlSession sqlSession = sqlSessionFactory.openSession();

        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
        List<User> userList = mapper.findAll();
        for (User user : userList) {
            System.out.println(user);
        }
        /*
        User{id=1, username='zhangsan', password='123', birthday=Sat Jul 24 20:00:29 CST 2021, orderList=[Order{id=1, ordertime=Thu Jan 01 08:00:02 CST 1970, total=3000.0, user=null}, Order{id=3, ordertime=Thu Jan 01 08:00:02 CST 1970, total=344.0, user=null}]}
        User{id=2, username='lisi', password='345', birthday=Sat Jul 24 20:00:29 CST 2021, orderList=[Order{id=2, ordertime=Thu Jan 01 08:00:02 CST 1970, total=1000.0, user=null}, Order{id=4, ordertime=Thu Jan 01 08:00:02 CST 1970, total=455.0, user=null}]}
        User{id=3, username='tom', password='abc', birthday=Sat Jul 24 20:00:29 CST 2021, orderList=[Order{id=5, ordertime=Thu Jan 01 08:00:02 CST 1970, total=100.0, user=null}]}
         */

        sqlSession.close();
    }