Mybatis多表关联查询字段值覆盖问题

错误展示

• 多表关联查询的返回结果集

	<resultMap id="specialdayAndWorktimeMap type="com.hierway.resm.domain.manage.timeSchedule.SpecialDayWorkTimeVO">  
  		<id column="special_date_id" property="specialDateId"/>
 		<result column="name" property="name"/>
  		<result column="date" property="date"/>
  		<result column="type" property="type"/>
  		<result column="start_time" property="startTime"/>
  		<result column="end_time" property="endTime"/>
  		<collection property="workTimeList" ofType="com.hierway.resm.domain.manage.timeSchedule.WorkTime">
    		<id column="work_time_id" property="workTimeId"/>
    		<result column="start_time" property="startTime"/>
   			<result column="end_time" property="endTime"/>
  		</collection>
	</resultMap>  

上面的映射中，返回结果类：SpecialDayWorkTimeVO中定义了7个属性，其中第7个属性是关联查询一对多的对象List。

可以看到在workTime中的属性startTime与endTime和上面的startTime与endTime属性名相同。

• 查询语句展示

	<select id="getSpecialDayAndWorkTimesByPuId" resultMap="specialdayAndWorktimeMap">
	  SELECT sd.special_date_id,sd.name,sd.type,sd.date,sd.start_time,sd.end_time,wt.work_time_id,wt.start_time,wt.end_time
	 FROM powerunit_specialday_relation AS psr
	  LEFT JOIN special_day AS sd ON psr.special_date_id = sd.special_date_id
	 LEFT JOIN specailday_worktime_relation AS swr ON sd.special_date_id = swr.special_date_id
	 LEFT JOIN work_time AS wt ON swr.work_time_id = wt.work_time_id
	 WHERE psr.pu_id = #{puId}
	</select>

在junit中进行mapper层测试，原本数据库中只有一条SpecialDay的记录，并没有关联的WorkTime记录，那么理想的结果是返回的VO对象中
specialDay相关的属性有值，而List是一个长度为0的List。可是测试结果转为Json格式如下所示：

[{"specialDateId":2,"name":"b","date":"2019-04-27","type":0,"startTime":"5:00","endTime":"17:00","workTimeList":[{"workTimeId":null,"startTime":"5:00","endTime":"17:00"}]}]

可以看到，list中含有一条数据，且前面的属性，覆盖了后面具有相同属性名的WorkTime中的startTime与endTime值，结果与测试结果不符合。

解决方案

• 给workTime表查询结果设置一个区分的别名，同时修改resultMap中标签下的对应的字段名（column元素），展示如下：

	<resultMap id="specialdayAndWorktimeMap" type="com.hierway.resm.domain.manage.timeSchedule.SpecialDayWorkTimeVO">
	    <id column="special_date_id" property="specialDateId"/>
	    <result column="name" property="name"/>
	    <result column="date" property="date"/>
	    <result column="type" property="type"/>
	    <result column="start_time" property="startTime"/>
	    <result column="end_time" property="endTime"/>
	    <collection property="workTimeList" ofType="com.hierway.resm.domain.manage.timeSchedule.WorkTime">
	      <id column="work_time_id" property="workTimeId"/>
	      <result column="wstart_time" property="startTime"/>
	      <result column="wend_time" property="endTime"/>
	    </collection>
	  </resultMap>  

	 <!--List<SpecialDayWorkTimeVO> getSpecialDayAndWorkTimesByPuId(Integer puId);-->
	 <select id="getSpecialDayAndWorkTimesByPuId" resultMap="specialdayAndWorktimeMap">
	    SELECT sd.special_date_id,sd.name,sd.type,sd.date,sd.start_time,sd.end_time,wt.work_time_id,wt.start_time AS wstart_time ,wt.end_time AS wend_time
	    FROM powerunit_specialday_relation AS psr
	    LEFT JOIN special_day AS sd ON psr.special_date_id = sd.special_date_id
	 LEFT JOIN specailday_worktime_relation AS swr ON sd.special_date_id = swr.special_date_id
	 LEFT JOIN work_time AS wt ON swr.work_time_id = wt.work_time_id
	 WHERE psr.pu_id = #{puId}
	</select>

• 相同测试数据如下：

[{"specialDateId":2,"name":"b","date":"2019-04-27","type":0,"startTime":"5:00","endTime":"17:00","workTimeList":[]}]  

此次测试结果正确！workTimeList长度为0。