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 -~----------~----~----~----~------~----~------~--~---
