MyBatis复杂映射开发之一对一查询

一对一查询需求

用户表和订单表的关系为：一个用户可以有多个订单，一个订单只能从属于一个用户

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一对一查询需求：查询一个订单，同时查询出该订单所对应的用户

对应的 sql 语句：select * from orders o,user u where o.uid=u.id

查询结果如下：

id	ordertime	total	uid	id	username	password	birthday
1	2022-03-17 17:15:33	3000	1	1	lucy	123	2022-03-17 17:15:56
2	2022-03-17 17:15:33	4000	1	1	lucy	123	2022-03-17 17:15:56
3	2022-03-17 17:15:33	5000	2	2	tom	123	2022-03-17 17:15:56

需求分析

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​

具体实现

创建 User 和 Order 实体

• User

  /**
   * 用户信息
   *
   * @name: User
   * @author: terwer
   * @date: 2022-03-17 17:41
   **/
  public class User {
      private Integer id;
      private String username;
  
      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;
      }
  
      @Override
      public String toString() {
          return "User{" +
                  "id=" + id +
                  ", username='" + username + '\'' +
                  '}';
      }
  }
  

• Order

  /**
   * 订单
   *
   * @name: Order
   * @author: terwer
   * @date: 2022-03-17 17:42
   **/
  public class Order {
      private Integer id;
      private String orderTime;
      private Double total;
  
      // 代表当前订单属于哪一个用户
      private User user;
  
      public Integer getId() {
          return id;
      }
  
      public void setId(Integer id) {
          this.id = id;
      }
  
      public String getOrderTime() {
          return orderTime;
      }
  
      public void setOrderTime(String orderTime) {
          this.orderTime = orderTime;
      }
  
      public Double getTotal() {
          return total;
      }
  
      public void setTotal(Double total) {
          this.total = total;
      }
  
      public User getUser() {
          return user;
      }
  
      public void setUser(User user) {
          this.user = user;
      }
  
      @Override
      public String toString() {
          return "Order{" +
                  "id=" + id +
                  ", orderTime='" + orderTime + '\'' +
                  ", total=" + total +
                  ", user=" + user +
                  '}';
      }
  }
  

创建 OrderMapper 接口

/**
 * 订单映射
 *
 * @name: IUserMapper
 * @author: terwer
 * @date: 2022-03-17 17:54
 **/
public interface OrderMapper {
    /**
     * 查询订单同时查询订单所属用户
     * @return
     */
    public List<Order> findOrderAndUser();
}

配置 OrderMapper.xml

<?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.terwergreen.mapper.OrderMapper">
    <resultMap id="orderMap" type="com.terwergreen.pojo.Order">
        <result property="id" column="id"></result>
        <result property="orderTime" column="ordertime"></result>
        <result property="total" column="total"></result>

        <association property="user" javaType="com.terwergreen.pojo.User">
            <result property="id" column="uid"></result>
            <result property="username" column="username"></result>
        </association>
    </resultMap>

    <!-- resultMap：手动配置实体属性与表字段的映射关系 -->
    <select id="findOrderAndUser" resultMap="orderMap">
        select * from orders o,user u where o.uid=u.id
    </select>
</mapper>

另外一种配置方法

 <mapper namespace="com.terwergreen.mapper.OrderMapper">
    <resultMap id="orderMap" type="com.terwergreen.pojo.Order">
       <result property="id" column="id"></result>
        <result property="orderTime" column="ordertime"></result>
        <result property="total" column="total"></result>
    
        <result property="user.id" column="uid"></result>
        <result property="user.username" column="username"></result>
    </resultMap>
  
    <!-- resultMap：手动配置实体属性与表字段的映射关系 -->
    <select id="findOrderAndUser" resultMap="orderMap">
        select * from orders o,user u where o.uid=u.id
    </select>
</mapper>

测试结果

@Test
public void test1() throws IOException {
    InputStream resourceAsStream = Resources.getResourceAsStream("sqlMapConfig.xml");
    SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(resourceAsStream);

    SqlSession sqlSession = sqlSessionFactory.openSession();
    OrderMapper orderMapper = sqlSession.getMapper(OrderMapper.class);

    List<Order> orderList = orderMapper.findOrderAndUser();
    for (Order order : orderList) {
        System.out.println(order);
    }
}

​

文章更新历史

2024/05/13 同步文章到其他平台

2022/05/08 feat: 初稿

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