Mybatis多表關聯查詢字段值覆蓋問題

錯誤展示

• 多表關聯查詢的返回結果集

	<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，返回結果類：SpecialDayWorkTimeVO中定義了7個屬性，其中第7個屬性是關聯查詢一對多的對象List 。

可以看到在workTime中的屬性startTime與endTime和上面的startTime與endTime屬性名相同。

• 查詢語句展示

	<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中進行mapper層測試，原本數據庫中只有一條SpecialDay的記錄，並沒有關聯的WorkTime記錄，那么理想的結果是返回的VO對象中
specialDay相關的屬性有值，而List 是一個長度為0的List。可是測試結果轉為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中含有一條數據，且前面的屬性，覆蓋了后面具有相同屬性名的WorkTime中的startTime與endTime值，結果與測試結果不符合。

解決方案

• 給workTime表查詢結果設置一個區分的別名，同時修改resultMap中 標簽下的對應的字段名（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>

• 相同測試數據如下：

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

此次測試結果正確！workTimeList長度為0。