[GitHub] [airflow] uranusjr commented on pull request #17924: Display ImportErrors from all readable DAGs

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

uranusjr commented on pull request #17924:
URL: https://github.com/apache/airflow/pull/17924#issuecomment-908920361


   ```python
   if (permissions.ACTION_CAN_READ, permissions.RESOURCE_DAG) in user_permissions:
   	import_errors = session.query(errors.ImportError).order_by(errors.ImportError.id).all()
   else:
   	# if the user doesn't have access to all DAGs, only display errors from visible DAGs
   	import_errors = (
   		session.query(errors.ImportError)
   		.join(DagModel, DagModel.fileloc == errors.ImportError.filename)
   		.filter(DagModel.dag_id.in_(filter_dag_ids))
   		.order_by(errors.ImportError.id)
   	).all()
   ```
   
   Since `import_errors` is only used for iteration in the subsequent `for` block, this can be made cleaner (and likely more performant) as:
   
   ```python
   import_errors = session.query(errors.ImportError).order_by(errors.ImportError.id)
   if (permissions.ACTION_CAN_READ, permissions.RESOURCE_DAG) not in user_permissions:
       import_errors = (
   		import_errors
   		.join(DagModel, DagModel.fileloc == errors.ImportError.filename)
   		.filter(DagModel.dag_id.in_(filter_dag_ids))
   	)
   ```
   
   A SQLAlchemy Query instnace is lazily iterable, so this avoids loading the ImportError objects into memory all at once, but one by one instead.


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