Mybatis进阶学习笔记——关系查询——一对多查询

一个客户拥有多个订单

    <resultMap type="User" id="UserOrderResultMap">
        <id column="id" property="id"/>
        <result column="name" property="name"/>
        
        <!-- 如何体现出User中封装的订单呢？需要用到collection标签 -->
        <!-- 
            collection：需要封装的集合
            property：关联属性的名字
         -->
        <!-- <collection property="orders" javaType="Order"> -->
        <!-- opType使用alt+/会自动提示 -->
        <collection property="orders" ofType="Order">
            <id column="order_id" property="id"/>
            <result column="orderno" property="orderno"/>
            <result column="productname" property="productname"/>
        </collection>
        
    </resultMap>
    
    <select id="queryUserOrder" resultMap="UserOrderResultMap">
        SELECT u.id,u.name,o.orderno,o.id order_id,o.productname FROM t_user u LEFT JOIN t_order o ON o.user_id=u.id
    </select>

User.java：

package cn.sm1234.domain;

import java.util.ArrayList;
import java.util.List;

public class User {

    private Integer id;
    private String name;
    private String password;
    
    private List<Order> orders = new ArrayList<Order>();
    
    public Integer getId() {
        return id;
    }
    public void setId(Integer id) {
        this.id = id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public String getPassword() {
        return password;
    }
    public void setPassword(String password) {
        this.password = password;
    }
    public List<Order> getOrders() {
        return orders;
    }
    public void setOrders(List<Order> orders) {
        this.orders = orders;
    }
    
    
}

package cn.sm1234.dao;

import java.util.List;

import cn.sm1234.domain.User;

public interface UserDao {

    public List<User> queryUserOrder();
}

    @Test
    public void test3() {
        SqlSession sqlSession = SessionUtils.getSession();
        // getMapper(): 返回指定接口的动态代理的实现类对象
        UserDao dao = sqlSession.getMapper(UserDao.class);
        List<User> userList = dao.queryUserOrder();
        for (User user : userList) {
            System.out.println("用户信息"+user.getId()+"-"+user.getName());
            for(Order order : user.getOrders()){
                System.out.println("订单信息"+order.getOrderno()+"-"+order.getProductname());
            }
        }
        sqlSession.commit();
        sqlSession.close();
    }

数据库信息：

测试查询结果：