Django postgresql notes

1. Do not "pass" on

   DatabseError

   exceptions in signal processors. Bad example:
   

   @receiver(post_save, sender=User, dispatch_uid='user_post_save')
   def user_post_save(sender, instance, created, raw, **kwargs):
       if created and not raw:
           try:
               try:
                   flatpage = FlatPage.objects.get(url='/my_page/')
               except FlatPage.DoesNotExist:
                   flatpage = FlatPage.objects.create(**DEFAULT_PAGE)
               user = instance
   
               notify.send(user, recipient=user, verb="flatpage", target=flatpage)
           except DatabaseError:
               pass
   

   
   I tried to use pass in this example because syncdb failes for sqlite and "passing" fixed that problem.
   But postgresql will still fail with "Transaction aborted" if you just pass this exception. You should rollback transaction to make it work:
   
   

   from django.db import transaction
   
   @receiver(post_save, sender=User, dispatch_uid='user_post_save')
   def user_post_save(sender, instance, created, raw, **kwargs):
       if created and not raw:
           with transaction.commit_on_success():
               try:
                   try:
                       flatpage = FlatPage.objects.get(url='/my_page/')
                   except FlatPage.DoesNotExist:
                       flatpage = FlatPage.objects.create(**DEFAULT_PAGE)
                   user = instance
   
                   notify.send(user, recipient=user, verb="flatpage", target=flatpage)
               except DatabaseError:
                   transaction.rollback()
   

   
   
2. If you use South then you could also encounter problems when one of your apps depends on migrations in other app. For example your

   clients.ContactPerson

   has FK to

   projects.Project

   and your

   projects.Project

   has FK to

   client.Client

   . In real situation this relations will be splited to several migrations and there should be at least one migration where

   clients

   app is not dependent on

   projects

   app or vice versa. In this case to make migrations work under postgresql, you should specify dependencies:
   
   

   class Migration:
       
       depends_on = (
           ("clients", "0001_initial"),
       )