MyBatis懒加载数据（大批量数据处理）

葵续浅笑2024-05-27 16:10

使用范例

Cursor约定使用Iterator去懒加载数据，以时间换空间，非常适合处理通常无法容纳在内存中的数百万个项目查询。如果在 resultMap 中使用集合，则必须使用 resultMap 的 id 列对游标 SQL 查询进行排序(resultOrdered="true")。

java 复制代码

//为了避免bug，手动管理一个session
try (SqlSession sqlSession = sqlSessionFactory.openSession()) {
    DDeviceShopIndexStatusMapper shopIndexStatusMapper = sqlSession.getMapper(DDeviceShopIndexStatusMapper.class);
    try (Cursor<DAlarmEventDTO> cursor = shopIndexStatusMapper.selectDevicesForShopClosed(commonProperties.getOpenShopStatus(), ABNORMAL.getCode())) {
        for (DAlarmEventDTO alarmEventDTO : cursor) {
            applicationContext.publishEvent(new DeviceShopClosedEvent(new Object(), alarmEventDTO));
        }
    } catch (IOException e) {
        log.error("shopStatusCheckJob cursor error:", e);
    }
}
============================
//方法定义
Cursor<DAlarmEventDTO> selectDevicesForShopClosed(@Param("shopStatus") List<String> shopStatus, @Param("status") Integer status);
============================
//xml写法与平常无异
<select id="selectDevicesForShopClosed" resultType="com.rome.device.monitor.admin.infrastructure.remote.dto.DAlarmEventDTO">
    select ddsb.device_key,
           ....
    from d_device_detail ddd
    left join d_device_shop_bind ddsb on ddd.device_key = ddsb.device_key
    ....
    where 
    ....
</select>