ris_dm/server/application/api/model/device/DeviceModel.php

<?php
namespace app\api\model\device;
use app\api\model\ZskkDefaultModel;
use think\facade\Log;


class DeviceModel extends ZskkDefaultModel {
  protected $table= 'device';
  protected $logName = "DeviceModel";

  public function getExamClass($deviceId) {
      $name = $this
          ->alias('d')
          ->join(['constant'=>'e'], 'd.exam_class_id = e.id')
          ->where('d.id',$deviceId)
          ->value('e.constant_value');
      return $name;
  }
}