Mybatis 不建实体类，将数据反给前端

MySQL 统计每个时间段的数量：https://www.cnblogs.com/vipsoft/p/19195343

在Mybatis中不建实体类，可以通过以下几种方式返回数据给前端：

Mapper接口

public interface VipSoftOrderMapper {
    List<Map<String, Object>> getTimePeriodStatistics();
}

Mapper XML

  <select id="getTimePeriodStatistics" resultType="java.util.Map">
    SELECT
      CONCAT(LPAD(hour_range, 2, '0'), ':00~', LPAD(hour_range + 1, 2, '0'), ':00') as timePeriod,
      SUM(CASE WHEN HOUR(start_time) = hour_range THEN 1 ELSE 0 END) as startCount,
      SUM(CASE WHEN HOUR(end_time) = hour_range THEN 1 ELSE 0 END) as endCount
    FROM
      custody_order,
      (SELECT 0 as hour_range UNION SELECT 1 UNION SELECT 2 UNION SELECT 3 UNION SELECT 4
       UNION SELECT 5 UNION SELECT 6 UNION SELECT 7 UNION SELECT 8 UNION SELECT 9
       UNION SELECT 10 UNION SELECT 11 UNION SELECT 12 UNION SELECT 13 UNION SELECT 14
       UNION SELECT 15 UNION SELECT 16 UNION SELECT 17 UNION SELECT 18 UNION SELECT 19
       UNION SELECT 20 UNION SELECT 21 UNION SELECT 22 UNION SELECT 23) hours
    GROUP BY
      hour_range
    ORDER BY
      hour_range;
  </select>

Service层

@Service
public class StatisticsService {
    
    @Autowired
    private VipSoftOrderMapper vipsoftOrderMapper;
    @Autowired
    private StringRedisTemplate redisTemplate;
    
    public List<Map<String, Object>> getTimePeriodStatistics() {
        List<Map<String, Object>> timePeriodStatistics = null;
        String redisKey = RedisKey.TIME_PERIOD_STATISTICS + "_" + DateTime.now().year();
        if (redisTemplate.hasKey(redisKey)) {
            String result = redisTemplate.opsForValue().get(redisKey);
            TypeReference<List<Map<String, Object>>> typeReference = new TypeReference<List<Map<String, Object>>>() {};
            timePeriodStatistics = com.alibaba.fastjson.JSON.parseObject(result,typeReference);
            return timePeriodStatistics;
        }

        timePeriodStatistics = vipsoftOrderMapper.getTimePeriodStatistics();
        String redisValue = PojoUtil.pojoToJson(timePeriodStatistics);
        redisTemplate.opsForValue().set(redisKey, redisValue);
        redisTemplate.expire(redisKey, 1, TimeUnit.DAYS);
        return timePeriodStatistics;
    }
}

Controller层

@RestController
@RequestMapping("/api/statistics")
public class StatisticsController {
    
    @Autowired
    private StatisticsService statisticsService;
    
    @GetMapping("/timePeriod")
    public ResponseEntity<List<Map<String, Object>>> getTimePeriodStatistics() {
        List<Map<String, Object>> result = statisticsService.getTimePeriodStatistics();
        return ResponseEntity.ok(result);
    }
}

前端接收的数据格式

[
  {
    "timePeriod": "00:00~01:00",
    "startCount": 0,
    "endCount": 0
  },
  {
    "timePeriod": "01:00~02:00", 
    "startCount": 0,
    "endCount": 0
  },
  {
    "timePeriod": "08:00~09:00",
    "startCount": 20,
    "endCount": 15
  },
  {
    "timePeriod": "09:00~10:00",
    "startCount": 35,
    "endCount": 19
  }
  // ... 其他时段
]

推荐方案

1. 不需要创建额外的实体类
2. 灵活性高，字段名直接在SQL中定义
3. Mybatis自动将结果映射到Map中
4. 前端可以直接使用返回的数据

这样就能在不建实体类的情况下，通过Mybatis将统计数据返回给前端了。