def fetch_next(self, query=None, **kwargs):
        """Generator to yield data one row at a time.
        Yields a Result, not the entire ResultSet. The containing ResultSet
        can be accessed through `Result.resultset`, but be careful not to
        manipulate the ResultSet until it is populated (when this generator
        is empty), or you may see unexpected results.
        """
        if query:
            self.query = query

        hash_ = self._hash
        if hash_ in self._data:
            for result in self._data[hash_]:
                yield result

        if self.scraper.current_item is not self:
            self._move_here()

        self._data[hash_] = ResultSet()
        self._data[hash_].dialect = self.dialect
        self._data[hash_].dataset = self
        for result in self.scraper._fetch_data(self,
                                               query=self.query,
                                               **kwargs):
            self._data[hash_].append(result)
            yield result