mybatis中mapper文件resultMap中collection和association的使用

最新推荐文章于 2025-07-10 20:20:31 发布

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最新推荐文章于 2025-07-10 20:20:31 发布

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本文详细解析了MyBatis框架中resultMap配置项的使用，包括collection和association属性的应用场景，通过具体示例展示了如何实现一对多和多对一的关系映射，适合于希望深入理解MyBatis数据映射机制的开发者。

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参考文章地址：https://www.cnblogs.com/stefanking/articles/5092474.html

mybatis mapper配置文件结果集映射resultMap中collection属性(一对多关系结果集映射)和association属性(多对一关系结果集映射)理解：

collection的使用有两种resultMap和select，必须手动指定一种

Mapper文件内容如下：

<?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.xi.mythymeleaf.dao.mapper.UserMapper">

    <!-- collection resultMap 方法 -->
    <!--<resultMap id="BaseResultMap" type="com.xi.mythymeleaf.dao.entity.User">
        <id column="id" property="id" />
        <result column="name" property="name" />
        <collection property="accounts" resultMap="accountMap" />
    </resultMap>

    <resultMap id="accountMap" type="com.xi.mythymeleaf.dao.entity.Account">
        <result column="aid" property="id" />
        <result column="user_id" property="userId" />
        <result column="num" property="num" />
    </resultMap>

    <select id="selectAll" resultMap="BaseResultMap">
              SELECT t.id, t.name as name, a.id as aid,a.user_id,a.num FROM user t
              RIGHT JOIN account a ON t.id=a.user_id
       </select>-->

    <!-- collection select 方法 -->
    <resultMap id="BaseResultMap" type="com.xi.mythymeleaf.dao.entity.User">
        <result column="id" property="id" />
        <result column="name" property="name" />
        <collection property="accounts" column="id" select="selectAccount" />
    </resultMap>

    <select id="selectAccount" resultType="com.xi.mythymeleaf.dao.entity.Account">
              SELECT id as id, user_id as userId, num as num FROM account
              WHERE user_id = #{id}
    </select>

    <select id="selectAll" resultMap="BaseResultMap">
              SELECT * FROM user t
    </select>


</mapper>

输出如下：

association(多对一结果集转换)的示例：

Mapper内容如下

<?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.xi.mythymeleaf.dao.mapper.AccountMapper">

    <!-- 通用查询映射结果 -->
    <resultMap id="BaseResultMap" type="com.xi.mythymeleaf.dao.entity.Account">
        <id column="id" property="id" />
        <result column="user_id" property="userId" />
        <result column="num" property="num" />
        <association property="user" resultMap="userMap" />
    </resultMap>

    <resultMap id="userMap" type="com.xi.mythymeleaf.dao.entity.User">
        <result column="tid" property="id" />
        <result column="name" property="name" />
    </resultMap>

    <insert id="insert" useGeneratedKeys="true" keyProperty="id">
              INSERT INTO account(user_id, num) VALUES(
                #{userId}, #{num}
              )
    </insert>

    <select id="selectAll" resultMap="BaseResultMap">
        SELECT a.id as id, t.id as tid, a.user_id as user_id, num as num, t.name as name  FROM account a
        LEFT JOIN user t on a.user_id = t.id
    </select>

</mapper>

输出如下：