Mark this update as complete.

def touch(self):
        """
        Mark this update as complete.
        """
        if self.marker_table_bound is None:
            self.create_marker_table()

        table = self.marker_table_bound
        id_exists = self.exists()
        with self.engine.begin() as conn:
            if not id_exists:
                ins = table.insert().values(update_id=self.update_id, target_table=self.target_table,
                                            inserted=datetime.datetime.now())
            else:
                ins = table.update().where(sqlalchemy.and_(table.c.update_id == self.update_id,
                                                           table.c.target_table == self.target_table)).\
                    values(update_id=self.update_id, target_table=self.target_table,
                           inserted=datetime.datetime.now())
            conn.execute(ins)
        assert self.exists()