我如何更好地处理Flask-SQLAlchemy提交/回滚？

Question

I'm reviewing some old code I wrote and was looking at a shared commit function I had written to handle responses to the user on certain failures when attempting to commit changes to the database (such as deletes):

def _commit_to_database():
    """A shared function to make a commit to the database and handle exceptions
    if encountered.
    """
    flask.current_app.logger.info('Committing changes to database...')
    try:
        db.session.commit()
    except AssertionError as err:
        flask.abort(409, err)
    except (exc.IntegrityError, sqlite3.IntegrityError) as err:
        flask.abort(409, err.orig)
    except Exception as err:
        flask.abort(500, err)
    finally:
        db.session.rollback()

I think I understand my thought process: attempt the commit , upon certain failures trigger a flask.abort to send the response back, but I believe I found that the database was left with an open session requiring a rollback when I did this and adding the rollback into a finally statement resolved this allowing me to still use the flask.abort .

The questions I have around me code are:

1) Is this a bug: will the Flask-SQLAlchemy extension not close out the session as normal; is calling the rollback on the finally which will be triggering after the abort going to affect successful commit s?

2) If this is a bug: what should I be doing differently in handling the try-except-finally and the db session?

Answer 1

You need to rollback when exception occurs and finally close the session:

def _commit_to_database(): 
    """A shared function to make a   
       commit to the database and
       handle exceptions if encountered.
    """
    flask.current_app.logger.info(
        'Committing changes to db...'
    )
    try: 
        db.session.commit() 
    except AssertionError as err:
        db.session.rollback()
        flask.abort(409, err) 
    except (
        exc.IntegrityError, 
        sqlite3.IntegrityError
     ) as err:
        db.session.rollback()
        flask.abort(409, err.orig) 
    except Exception as err:
        db.session.rollback()
        flask.abort(500, err) 
    finally: 
        db.session.close()