public static function getByUserId($uid)
 {
     /**
      * @var $db \PDO
      */
     global $db;
     // Prepare SELECT
     $stmt = $db->prepare("SELECT `id` FROM " . self::$tableName . " WHERE user = ?");
     $stmt->execute(array($uid));
     if ($stmt->rowCount() == 0) {
         throw new MailSubscriptionNotFoundException();
     }
     $dataFromDB = $stmt->fetch(\PDO::FETCH_ASSOC);
     $mailSubscription = MailSubscription::getById($dataFromDB['id']);
     return $mailSubscription;
 }