On 16 heinä, 14:00, "Cal Leeming [Simplicity Media Ltd]" <[email protected]> wrote: > Hi guys, > > Okay so, this has been marked as wontfix in its current approach. > > The problem exists purely because of the way MySQL transactions and indexes > work - if you create a row that matches a unique index, it won't show up as > a row until you commit (which is correct), but if you try and insert > another row that matches this same unique index it will say the key already > exists (this is to prevent unique constraint race conditions within > transactions). > > This really isn't a bug in the code, but more that developers need to > understand how the database works, and take the appropriate actions (in > this case, it's that you need to commit() the transaction to guarantee safe > usage of get_or_create()). > > As aaugustin brought up, we can't automatically commit as this would break > transaction control, and there is little point in adding a 'commit=True' > argument onto get_or_create() because you could just do this yourself. > > Therefore, I'm proposing a documentation update that highlights and > explains this in a clear and simple way - rather than any sort of code > change. Would this be an appropriate way forward?
I have tried different ways of solving this issue. To me it seems that unless one does a commit in get_or_create or changes the default isolation level used by MySQL then there is no cure for this issue. And this issue seems to pop out regularly. I don't the above mentioned approaches as good solutions. I would like to see the possibility to use different isolation levels if the user chooses so. This would be a good solution in my opinion: use READ COMMITTED isolation level if you are having problems with get_or_create. Allowing use of different isolation levels has other advantages, too. The use of custom isolation level should come with a big warning of "you should know what you are doing, or prepare for trouble". So, lets document the current behavior for now, and check if we can do something to the isolation level issue later on. - Anssi -- You received this message because you are subscribed to the Google Groups "Django developers" group. To post to this group, send email to [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit this group at http://groups.google.com/group/django-developers?hl=en.
