public function update_batch($data, $where_key)
    {
        $_data = array();

        foreach ($data as $key => $row) {

            if (false !== $row = $this->_do_pre_update($row)) {
                $_data[$key] = $row;
            }
        }

        return $this->_database->update_batch($this->_table, $_data, $where_key);
    }