def read_item(self, from_date=None):
        """Read items and return them one by one.

        :param from_date: start date for incremental reading.
        :return: next single item when any available.
        :raises ValueError: `metadata__timestamp` field not found in index
        :raises NotFoundError: index not found in ElasticSearch
        """
        search_query = self._build_search_query(from_date)
        for hit in helpers.scan(self._es_conn,
                                search_query,
                                scroll='300m',
                                index=self._es_index,
                                preserve_order=True):
            yield hit
Read items and return them one by one.

        :param from_date: start date for incremental reading.
        :return: next single item when any available.
        :raises ValueError: `metadata__timestamp` field not found in index
        :raises NotFoundError: index not found in ElasticSearch