On 21 sept. 2013, at 15:53, Richard Ward <[email protected]> wrote:

> I'm OK with trying to to raise exceptions when making a query and 
> get_rollback returns True. I'm not sure it's doable; patch welcome ;-) 
> 
> How about this: 
> https://github.com/RichardOfWard/django/commit/cb46c75db275db59b54511c090286255bd9cc46d
> 
> It raises the same error that PostgreSQL would raise if you try and do any 
> SQL when in a transaction with 'needs_rollback' is True. I've tested this 
> with PostgreSQL, MySQL and SQLite3, and they all now behave in the same way 
> that PostgreSQL behave currently (I'm running the test suite at the moment, 
> its taking a while).

I wrote a patch based on this idea and unfortunately it doesn't work:
https://code.djangoproject.com/attachment/ticket/21134/21134-failed-attempt.patch

This patch triggers a large number of failures in the tests, because it 
prevents some read queries which are currently allowed. You didn't notice 
because your patch only works when DEBUG = True and the test suite runs with 
DEBUG = False.

If we step back from the implementation, the issue here is that MySQL and 
Oracle implicitly add a savepoint before each query, and under some 
circumstances implicitly rollback to that savepoint. This behavior allows 
transaction management schemes that don't map well to a context manager / 
decorator API like Django's.  See also 
https://code.djangoproject.com/ticket/11156#comment:14 which has the same root 
cause.

I made a significant effort trying to implement the suggestions in this thread 
and didn't obtain any results. If someone still wants to change something in 
this area, please write a patch with tests; I will review it.

-- 
Aymeric.




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