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：