Mybatis使用record类作为返回值时，值映射错误问题

问题描述

record类：

/**
 * 资产组统计record
 */
public record AssetGroupIdRecord(Long groupId, Integer num) {


}

Mapper方法：

    /**
     * 根据资产组统计数量
     * @param channelId 渠道id
     * @return List<AssetGroupIdRecord>
     */
    @MapKey("groupId")
    Map<Long, AssetGroupIdRecord> selectAssetGroupNum(Long channelId);

sql:

    <select id="selectAssetGroupNum" resultType="org.asset.record.AssetGroupIdRecord">
        select count(*) as num, GROUP_ID as groupId from asset where channel_id = #{channelId} and deleted_at = 0
            and history_flag = 0
        group by GROUP_ID

    </select>

出现的情况是,groupId和num这两个字段的值互换了

问题解决：

将argNameBasedConstructorAutoMapping参数设置为true即可解决上述问题。
在mybatis配置文件中添加配置：

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE configuration
        PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>

    <settings>

        <setting name="argNameBasedConstructorAutoMapping" value="true"/>
    </settings>

</configuration>

源码解析

在DefaultResultSetHandler处理类中，在调用构造函数初始化时会调用以下代码：

  private Object applyConstructorAutomapping(ResultSetWrapper rsw, ResultMap resultMap, String columnPrefix,
      Class<?> resultType, List<Class<?>> constructorArgTypes, List<Object> constructorArgs, Constructor<?> constructor)
      throws SQLException {
    boolean foundValues = false;
	//根据构造方法中参数名字去映射sql数据
    if (configuration.isArgNameBasedConstructorAutoMapping()) {
      foundValues = applyArgNameBasedConstructorAutoMapping(rsw, resultMap, columnPrefix, constructorArgTypes,
          constructorArgs, constructor, foundValues);
    } else {
	//根据构造方法中参数的顺序去映射sql数据
      foundValues = applyColumnOrderBasedConstructorAutomapping(rsw, constructorArgTypes, constructorArgs, constructor,
          foundValues);
    }
    return foundValues || configuration.isReturnInstanceForEmptyRow()
        ? objectFactory.create(resultType, constructorArgTypes, constructorArgs) : null;
  }

如果根据顺序去映射sql数据，就会出现上述的问题。