'The previous, SCHEDULED DagRun, if there is one'

@provide_session
def get_previous_scheduled_dagrun(self, session=None):

    dag = self.get_dag()
    return session.query(DagRun).filter((DagRun.dag_id == self.dag_id), (DagRun.execution_date == dag.previous_schedule(self.execution_date))).first()
