[GitHub] ashb commented on a change in pull request #4528: [AIRFLOW XXX] adding exception catch to trigger_dag api

[GitBox <gi...@apache.org>]

ashb commented on a change in pull request #4528: [AIRFLOW XXX] adding exception catch to trigger_dag api
URL: https://github.com/apache/airflow/pull/4528#discussion_r248059306
 
 

 ##########
 File path: airflow/api/common/experimental/trigger_dag.py
 ##########
 @@ -57,6 +58,12 @@ def _trigger_dag(
             dag_id
         ))
 
+    if UniqueExecutionDate and dag_run.find(dag_id=dag_id, execution_date=execution_date):
+        raise ExecutionDateAlreadyExists("Execution date {} already exists for dag id {}".format(
+            execution_date,
+            dag_id
+        ))
 
 Review comment:
   This sort of pattern (of check for unique then insert) is prone to race conditions and isn't perfect. The only sure fire way to guarantee uniqueness is to have a DB constraint and handle the constraint violation that the DB will raise.

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