工作中遇到这么一个问题，嵌套查询，返回json的时候，作为属性，deviceFields是一个device中的一个对象属性，在json返回的时候想要得到的应该是deviceFields:{ 具体属性}

但是实际上我发现我返回的确实  deviceFields:[{ 具体属性}],多了个中括号

这明显是把查询的结果作为了一个集合，而没有映射为一个对象，仔细查看，原来是在association上应该添加上javaType的对应的对象路径，而我把这个给漏掉了。下面是正确的

<resultMap type="map" id="getDeviceListResult">

<result property="deviceId" column="deviceId"/>
  <association property="deviceFields" column="deviceId" javaType="com.xxx.cloud.entity.DeviceFields" select="com.xxx.cloud.dao.DeviceFieldsMapper.selectByDeviceId"></association>
  <collection property="pointDataList"  column="deviceId" select="selectxxxDevicePointDataList"></collection>
  </resultMap>

<select id="getDeviceListByUserId" parameterType="map" resultMap="getDeviceListResult">

SELECT d.id deviceId,d.device_no deviceNo,d.gateway_uid uid,d.ext_addr extAddr,d.endpoint 'endpoint',d.device_name deviceName,
  device_type 'type',d.sub_device_type subType,d.product_id productId,d.company_id companyId,d.model model,d.version 'version',
  d.start_time startTime,d.del_flag delFlag 
  FROM d_device d, d_device_fields f,d_device_user_bind dub
  WHERE f.del_flag=0
  AND d.del_flag=0
  AND dub.del_flag=0
  AND d.company_id=#{companyId} 
  AND d.`product_id`=#{productId}
  AND d.id=f.device_id
  AND d.gateway_uid = dub.uid
  AND dub.user_id=#{userId}
  <if test="status != null">
      AND f.`online`=#{status}
      </if>
      <if test="rent != null and rent == 0">
      AND f.`rent` IS NULL
      </if>
      <if test="rent != null and rent != 0">
      AND f.`rent` = #{rent}
      </if>
      <if test="content != null">
      AND ( d.device_name like #{content}  OR d.model like #{content})
      </if>
            <if test="pointStatus != null">
      AND EXISTS (
SELECT 1
FROM d_device_point_data dpd
WHERE dpd.device_id = d.id
      AND dpd.del_flag = 0
      AND dpd.point_index = 23
      AND dpd.value = #{pointStatus}
)
      </if> order by f.online desc
  </select>