def num_dml_affected_rows(self):
        """Return the number of DML rows affected by the job.

        See:
        https://cloud.google.com/bigquery/docs/reference/rest/v2/jobs#statistics.query.numDmlAffectedRows

        :rtype: int or None
        :returns: number of DML rows affected by the job, or None if job is not
                  yet complete.
        """
        result = self._job_statistics().get("numDmlAffectedRows")
        if result is not None:
            result = int(result)
        return result