Run another DAG with TriggerDagRunOperator multiple times

Question

i have a DAG (DAG1) where i copy a bunch of files. I would then like to kick off another DAG (DAG2) for each file that was copied. As the number of files copied will vary per DAG1 run, i would like to essentially loop over the files and call DAG2 with the appropriate parameters.

eg:

with DAG( 'DAG1',
        description="copy files over",
        schedule_interval="* * * * *",
        max_active_runs=1
    ) as dag:


    t_rsync = RsyncOperator( task_id='rsync_data',
        source='/source/',
        target='/destination/' )

    t_trigger_preprocessing = TriggerDagRunOperator( task_id='trigger_preprocessing',
        trigger_daq_id='DAG2',
        python_callable=trigger

    )

    t_rsync >> t_trigger_preprocessing

i was hoping to use the python_callable trigger to pull the relevant xcom data from t_rsync and then trigger DAG2; but its not clear to me how to do this.

i would prefer to put the logic of calling DAG2 here to simplify the contents of DAG2 (and also provide stacking schematics with the max_active_runs)

Answer 1

ended up writing my own operator:

class TriggerMultipleDagRunOperator(TriggerDagRunOperator):
    def execute(self, context):
        count = 0
        for dro in self.python_callable(context):
            if dro:
                with create_session() as session:
                    dbag = DagBag(settings.DAGS_FOLDER)
                    trigger_dag = dbag.get_dag(self.trigger_dag_id)
                    dr = trigger_dag.create_dagrun(
                        run_id=dro.run_id,
                        state=State.RUNNING,
                        conf=dro.payload,
                        external_trigger=True)
                    session.add(dr)
                    session.commit() 
                    count = count + 1
            else:
                self.log.info("Criteria not met, moving on")
        if count == 0:
            raise AirflowSkipException('No external dags triggered')

with a python_callable like

def trigger_preprocessing(context):
    for base_filename,_ in found.items():
        exp = context['ti'].xcom_pull( task_ids='parse_config', key='experiment')
        run_id='%s__%s' % (exp['microscope'], datetime.utcnow().replace(microsecond=0).isoformat())
        dro = DagRunOrder(run_id=run_id) 
        d = { 
            'directory': context['ti'].xcom_pull( task_ids='parse_config', key='experiment_directory'),
            'base': base_filename,
            'experiment': exp['name'],
        }
        LOG.info('triggering dag %s with %s' % (run_id,d))
        dro.payload = d
        yield dro
    return

and then tie it all together with:

t_trigger_preprocessing = TriggerMultipleDagRunOperator( task_id='trigger_preprocessing',
    trigger_dag_id='preprocessing',
    python_callable=trigger_preprocessing
)