def create(self, reference, document_data):
        """Add a "change" to this batch to create a document.

        If the document given by ``reference`` already exists, then this
        batch will fail when :meth:`commit`-ed.

        Args:
            reference (~.firestore_v1beta1.document.DocumentReference): A
                document reference to be created in this batch.
            document_data (dict): Property names and values to use for
                creating a document.
        """
        write_pbs = _helpers.pbs_for_create(reference._document_path, document_data)
        self._add_write_pbs(write_pbs)