public function usePromotion($qrCode)
    {
        $promotionQR = substr($qrCode, 0, 10);
        $userID = substr($qrCode, 10);
        $promotionID = DB::table('publishpromotion')->select('id')->where('qrID', $promotionQR)->first();
        if ($promotionID != NULL) {
            return DB::table('promotionusage')->insert(['userID' => $userID, 'promotionID' => $promotionID->id]);
        }
        return false;
    }