public function update()
      {
            $fields = get_object_vars($this);
            $mask = [];
            $data = [];
            foreach ($fields as $name => $value){
                  if($name == 'id') {
                        continue;
                  }
                  $mask[$name . ' = :' . $name] = null;
                  $data[':' . $name] = $value;
            }
            $data[':id'] = $this->id;
            $sql = 'UPDATE ' .
                    static::TABLE . ' SET ' . implode(', ', array_keys($mask)) . ' WHERE id = :id';
            $db = new Db();
            $db->execute($sql, $data);

      }