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**Description**

Airflow 1.10 support providing a run_id to TriggerDagRunOperator using [DagRunOrder](https://github.com/apache/airflow/blob/v1-10-stable/airflow/operators/dagrun_operator.py#L30-L33) object that will be returned after calling [TriggerDagRunOperator#python_callable](https://github.com/apache/airflow/blob/v1-10-stable/airflow/operators/dagrun_operator.py#L88-L95). With https://github.com/apache/airflow/pull/6317 (Airflow 2.0), this behavior changed and one could not provide run_id anymore to the triggered dag, which is very odd to say the least.

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**Use case / motivation**

I want to be able to provide run_id for the TriggerDagRunOperator. In my case, I use the TriggerDagRunOperator to trigger 30K dag_run daily and will be so annoying to see them having unidentifiable run_id.

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After discussing with @ashb
**Suggested fixes can be**
 * provide a templated run_id as a parameter to TriggerDagRunOperator.
 * restore the old behavior of Airflow 1.10, where DagRunOrder holds the run_id and dag_run_conf of the triggered dag
 * create a new sub-class of TriggerDagRunOperator to fully customize it

**Are you willing to submit a PR?**

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**Related Issues**

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tests/operators/test_trigger_dagrun.py
"""Test TriggerDagRunOperator."""
        task = TriggerDagRunOperator(task_id="test_task", trigger_dag_id=TRIGGERED_DAG_ID, dag=self.dag)
        task.run(start_date=DEFAULT_DATE, end_date=DEFAULT_DATE, ignore_ti_state=True)
        with create_session() as session:
            dagruns = session.query(DagRun).filter(DagRun.dag_id == TRIGGERED_DAG_ID).all()
            assert len(dagruns) == 1
            assert dagruns[0].external_trigger
    def test_trigger_dagrun_with_execution_date(self):
        """Test TriggerDagRunOperator with custom execution_date."""
        utc_now = timezone.utcnow()
        task = TriggerDagRunOperator(
            task_id="test_trigger_dagrun_with_execution_date",
            trigger_dag_id=TRIGGERED_DAG_ID,
            execution_date=utc_now,
            dag=self.dag,
        )
        task.run(start_date=DEFAULT_DATE, end_date=DEFAULT_DATE, ignore_ti_state=True)
        with create_session() as session:
            dagruns = session.query(DagRun).filter(DagRun.dag_id == TRIGGERED_DAG_ID).all()
            assert len(dagruns) == 1
            assert dagruns[0].external_trigger
            assert dagruns[0].execution_date == utc_now
    def test_trigger_dagrun_twice(self):