def save(self, to_save, **kwargs):
        """save method
        """
        check = kwargs.pop('check', True)
        if check:
            self._valid_record(to_save)
        if '_id' in to_save:
            self.__collect.replace_one(
                {'_id': to_save['_id']}, to_save, **kwargs)
            return to_save['_id']
        else:
            result = self.__collect.insert_one(to_save, **kwargs)
            return result.inserted_id
save method