code: def list_documents(
          self,
          parent,
          collection_id,
          page_size=None,
          order_by=None,
          mask=None,
          transaction=None,
          read_time=None,
          show_missing=None,
          retry=google.api_core.gapic_v1.method.DEFAULT,
          timeout=google.api_core.gapic_v1.method.DEFAULT,
          metadata=None,
      ):
          if "list_documents" not in self._inner_api_calls:
              self._inner_api_calls[
                  "list_documents"
              ] = google.api_core.gapic_v1.method.wrap_method(
                  self.transport.list_documents,
                  default_retry=self._method_configs["ListDocuments"].retry,
                  default_timeout=self._method_configs["ListDocuments"].timeout,
                  client_info=self._client_info,
              )
          google.api_core.protobuf_helpers.check_oneof(
              transaction=transaction, read_time=read_time
          )
          request = firestore_pb2.ListDocumentsRequest(
              parent=parent,
              collection_id=collection_id,
              page_size=page_size,
              order_by=order_by,
              mask=mask,
              transaction=transaction,
              read_time=read_time,
              show_missing=show_missing,
          )
          iterator = google.api_core.page_iterator.GRPCIterator(
              client=None,
              method=functools.partial(
                  self._inner_api_calls["list_documents"],
                  retry=retry,
                  timeout=timeout,
                  metadata=metadata,
              ),
              request=request,
              items_field="documents",
              request_token_field="page_token",
              response_token_field="next_page_token",
          )
          return iterator