commit_on_success: Handle Exception in commit()

[Thomas Güttler]

If you get an exception during the commit done by the commit_on_success decorator, you get a meaningless error message:

django.db.transaction.TransactionManagementError: Transaction managed block ended with pending COMMIT/ROLLBACK

With this patch you see the real exception.

Can someone please write a unittest for this?

[Gabriel Hurley]

The reason for the problem is clear enough: The error raised in the finally clause overrides the original error.

However, I tried for about 2 hours to reproduce the reported bug with no success.

guettli, can you some information about the code you're using that triggers the bug?

[Thomas Güttler]

Hi Gabriel,

thank you for your question. This script results in

Traceback (most recent call last):
  File "djangotest_tbz/script.py", line 10, in <module>
    main()
  File "/home/djangotest_tbz_d/django/db/transaction.py", line 310, in _commit_on_success
    leave_transaction_management(using=db)
  File "/home/djangotest_tbz_d/django/db/transaction.py", line 87, in leave_transaction_management
    raise TransactionManagementError("Transaction managed block ended with pending COMMIT/ROLLBACK")
django.db.transaction.TransactionManagementError: Transaction managed block ended with pending COMMIT/ROLLBACK

I just tried it with latest trunk ([12761]). Postgres (psycopg2) evaluates Foreign-Key
Constraints lazy (deferrable). If you break this constraint, you get an exception
during commit. But you don't see the real problem.

from django.db import transaction, connection

@transaction.commit_on_success
def main():
    cursor=connection.cursor()
    cursor.execute('INSERT INTO auth_user_groups VALUES (DEFAULT, 10000000, 1000000);')
    transaction.set_dirty()

if __name__=='__main__':
    main()

[Gabriel Hurley]

Updates patch to work w/ MultiDB and adds tests

[Gabriel Hurley]

This specific bug seems to be backend-specific (it seems to be completely impossible to trigger it using SQLite3). I did manage to duplicate it, test it, and patch it using a server running psycopg2. The general principle of the fix seems universally applicable, though.

The patch I added has both the requested test and an updated version of the original patch that works with the new MultiDB in 1.2. Hopefully it's good to go now.

[Thomas Güttler]

Your patch is simple, contains a test and works for me. Thank you. Who can review and commit it?

[Russell Keith-Magee]

(In [12764]) Fixed #11900 -- Corrected an edge case of transaction handling in the commit_on_success decorator. Thanks to guettli for the report, and Gabriel Hurley for the initial test case.

[Jacob]

Milestone 1.2 deleted