Get the results for a given stream

        :param time_interval: The time interval
        :param stream: The stream object
        :return: A generator over stream instances

def get_results(self, stream, time_interval):
        """
        Get the results for a given stream

        :param time_interval: The time interval
        :param stream: The stream object
        :return: A generator over stream instances
        """
        query = stream.stream_id.as_raw()
        query['datetime'] = {'$gt': time_interval.start, '$lte': time_interval.end}
        with switch_db(StreamInstanceModel, 'hyperstream'):
            for instance in StreamInstanceModel.objects(__raw__=query):
                yield StreamInstance(timestamp=instance.datetime, value=instance.value)