docs: def transfer(cls, field_mappings, source, destination_factory):
      """Convert a record to a dictionary via field_mappings, and pass that to destination_factory."""
      data = dict()
      for index, field_mapping in enumerate(field_mappings):
        try:
          data[field_mapping.destination_name] = field_mapping.get_value(source)
        except Exception as ex:
          raise Exception(
            "Error with mapping #{0} '{1}'->'{2}': {3}".format(
              index,
              field_mapping.source_name,
              field_mapping.destination_name, ex)) from ex
      return destination_factory(data)