Ok, I'd rather handle it on the database level. Is that just a matter of creating a function and calling it on insert?
Koen On Apr 13, 4:47 am, "Ants Aasma" <[EMAIL PROTECTED]> wrote: > On Apr 13, 2:47 am, Jorge Godoy <[EMAIL PROTECTED]> wrote: > > > IF you insist on doing that at your code, make the column UNIQUE (or a > > PK...) and write something like this pseudocode: > > > def save_data(): > > def insert_data(): > > try: > > unique_column_value = get_max_from_unique_column > > Class(unique_column_value + 1, 'other data') > > except YourDBExceptionForConstraintViolation: > > sleep(random.random()) > > insert_data() > > > The 'sleep(random.random())' is there to avoid constant clashes and to > > be "fair" to all connections that are inserting data on your table. > > To get an uninterrupted number sequence you need to serialize your > inserts to that specific entity, for which you basically need locking. > The quoted approach is optimistic locking, where you hope that no one > tries to insert another row between when you use the > get_max_from_unique_column and do the database commit, but are ready > to retry if that expectation fails. Another way would be to use > pessimistic locking, by doing the get_max_from_unique_column query > with lockmode='update'. Then any other thread trying to insert another > row while you're busy inserting yours will have to wait. --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "sqlalchemy" 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/sqlalchemy?hl=en -~----------~----~----~----~------~----~------~--~---
