Questions regarding transactions on psycopg2
Question:
If I have a transaction that saves data in the database, but this transaction is part of another transaction that needs the id(fk) of that data to create a new data, but an error occurs at that moment, all transactions are rolled back or just the last transaction?
Answers:
They will both rollback unless you set up savepoints. A transaction "within transaction" is actually the same transaction. A plain ROLLBACK will revert everything, even if there are savepoints set up. A ROLLBACK TO savepoint will only undo operations that occured from that point onwards, keeping everything that took effect beforehand, still within the same transaction.
Here’s a demo – observe the state of the table compared to transaction id.
Psycopg2 lets you cur.execute('SAVEPOINT s1'), then cur.execute('ROLLBACK TO s1').
If I have a transaction that saves data in the database, but this transaction is part of another transaction that needs the id(fk) of that data to create a new data, but an error occurs at that moment, all transactions are rolled back or just the last transaction?
They will both rollback unless you set up savepoints. A transaction "within transaction" is actually the same transaction. A plain ROLLBACK will revert everything, even if there are savepoints set up. A ROLLBACK TO savepoint will only undo operations that occured from that point onwards, keeping everything that took effect beforehand, still within the same transaction.
Here’s a demo – observe the state of the table compared to transaction id.
Psycopg2 lets you cur.execute('SAVEPOINT s1'), then cur.execute('ROLLBACK TO s1').