/**
  * @return mixed
  */
 public static function getBulletinList($campaignId)
 {
     $fields = ['id', 'name', 'start_at', 'ended_at'];
     $bulletins = Bulletin::select($fields)->where('campaign_id', '=', $campaignId)->orderBy('id', 'asc')->get();
     return $bulletins;
 }