public function GetUniqueKey($uniqueKey)
 {
     try {
         $db = $this->connection();
         $sql = "SELECT * FROM " . self::$dbTable . " WHERE " . self::$uniqueKey . " = ?";
         $params = array($uniqueKey);
         $query = $db->prepare($sql);
         $query->execute($params);
         $result = $query->fetch();
         if ($result) {
             $user = new User();
             // Set my UserID and Expire to my dbUserModel.
             $user->SetUserID($result[self::$userID]);
             $user->SetExpire($result[self::$expire]);
             return $user;
         } else {
             return NULL;
         }
     } catch (\PDOException $e) {
         throw new \Exception();
     }
 }