Converts a batch of StatEntry value to ExportedFile values at once.

    Args:
      metadata_value_pairs: a list or a generator of tuples (metadata, value),
        where metadata is ExportedMetadata to be used for conversion and value
        is a StatEntry to be converted.
      token: Security token:

    Yields:
      Resulting ExportedFile values. Empty list is a valid result and means that
      conversion wasn't possible.

def BatchConvert(self, metadata_value_pairs, token=None):
    """Converts a batch of StatEntry value to ExportedFile values at once.

    Args:
      metadata_value_pairs: a list or a generator of tuples (metadata, value),
        where metadata is ExportedMetadata to be used for conversion and value
        is a StatEntry to be converted.
      token: Security token:

    Yields:
      Resulting ExportedFile values. Empty list is a valid result and means that
      conversion wasn't possible.
    """
    if data_store.RelationalDBEnabled():
      result_generator = self._BatchConvertRelational(metadata_value_pairs)
    else:
      result_generator = self._BatchConvertLegacy(
          metadata_value_pairs, token=token)

    for r in result_generator:
      yield r