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

• Order

创建OrderMapper接口

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

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文章更新历史
2022/05/08 feat:新增Kotlin支持

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