mybatis多表关联查询(一对多)

一 概述

一个用户可以拥有多个订单，可以在用户pojo类中添加一个泛型为Orders的集合
方法：
1.映射文件中使用resultMap配置
2. 用户表中加List< Orders > orderList属性

二 案例代码

目标：查询指定用户的订单

1.写sql语句

SELECT u.id,u.username,o.id oid,o.number,o.createtime,o.note from user u LEFT JOIN orders o on u.id=o.user_id and u.id=1

2. pojo类（user类添加订单list）

public class User implements Serializable {
    private Integer id;
    private String username;// 用户姓名
    private String sex;// 性别
    private Date birthday;// 生日
    private String address;// 地址
    private List orders;
    public List getOrders() {
        return orders;
    }
    public void setOrders(List orders) {
        this.orders = orders;
    }
    public Integer getId() {
        return id;
    }
    public void setId(Integer id) {
        this.id = id;
    }
    public String getUsername() {
        return username;
    }
    public void setUsername(String username) {
        this.username = username;
    }
    public String getSex() {
        return sex;
    }
    public void setSex(String sex) {
        this.sex = sex;
    }
    public Date getBirthday() {
        return birthday;
    }
    public void setBirthday(Date birthday) {
        this.birthday = birthday;
    }
    public String getAddress() {
        return address;
    }
    public void setAddress(String address) {
        this.address = address;
    }
    @Override
    public String toString() {
        return "User [id=" + id + ", username=" + username + ", sex=" + sex
                + ", birthday=" + birthday + ", address=" + address + "]";
    }




}

3.映射文件配置sql语句

<resultMap type="User" id="UserOrderResultMap">
        <id property="id" column="id"/>
        <result property="username" column="username"/>

        
        <collection property="orders" ofType="Orders">
            <id property="id" column="oid"/>
            <result property="number" column="number"/>
            <result property="createtime" column="createtime"/>
            <result property="note" column="note"/>
        collection>
    resultMap>
    
    <select id="findUserWithOrders" parameterType="int" resultMap="UserOrderResultMap">
        SELECT 
            u.id,
            u.username,
            o.id oid,
            o.number,
            o.createtime,
            o.note
        from user u 
        LEFT JOIN orders o 
        on u.id=o.user_id and u.id=#{id}
    select>

4.接口中定义对应方法

public interface UserDao {
//  public List findUserByQueryVo(QueryVo queryVo);
    public List findUserWithOrders(int id);
}

5.测试

package com.itheima.test;

import java.io.IOException;
import java.io.InputStream;
import java.util.ArrayList;
import java.util.List;

import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import org.junit.Before;
import org.junit.Test;

import com.itheima.domain.OrderWithCutomer;
import com.itheima.domain.Orders;
import com.itheima.domain.QueryVo;
import com.itheima.domain.User;
import com.itheima.mapperTest.OrdersDao;
import com.itheima.mapperTest.UserDao;

public class UserOperateTest2 {

    private SqlSessionFactory sqlSessionFactory;
    @Before
    public void setSqlSession() throws Exception{
        //1.获得SqlSession对象
        SqlSessionFactoryBuilder sqlSessionFactoryBuilder = new SqlSessionFactoryBuilder();
        InputStream inputStream = Resources.getResourceAsStream("SqlMapConfig.xml");
        sqlSessionFactory = sqlSessionFactoryBuilder.build(inputStream);
    }

    @Test
    public void testFindOrderWithCustomer() throws Exception{
        //1.获得SqlSession对象
        SqlSession sqlSession = sqlSessionFactory.openSession();
        //2.获得接口的代理对象   sqlSession.getMapper()
        UserDao userDao = sqlSession.getMapper(UserDao.class);
        //3.使用代理对象的方法操作
        List userWithOrders = userDao.findUserWithOrders(1);
        for (User user : userWithOrders) {
            System.out.println(user.getUsername());
            List orders = user.getOrders();
            for (Orders orders2 : orders) {
                System.out.println(orders2);
            }
        }
        //4.释放资源
        sqlSession.close();
    }
}