On Thu, Feb 4, 2010 at 8:08 PM, Jared Smith <jaredtsm...@gmail.com> wrote:
> My use case is that I'll have multiple users trying to update a set of > objects and I want to make sure that any user committing a change has > knowledge of the existing state. I was going to model that with a version > number so an update would look like: > > update table set col=foo, col1=bar where id=pknum && > version_number=<version I read> > > Desired result are the following:: > > --If a user has the correct previous version the update goes through > --if they don't have the correct previous version it should do nothing > (I'll throw an exception or return something to the upper layer to indicate > the fact that the user needs to try again from the latest version...) > > My question is how can I do an update like the above in Django? > http://docs.djangoproject.com/en/dev/topics/db/queries/#updating-multiple-objects-at-once Though it sounds like you do not want to update multiple at once, you can use the same call and know based on its returned value (it returns how many rows it updated) whether it worked or not. If one is returned, you know the version read was unchanged for the update and all is fine. If zero is returned then apparently someone else changed the row in the meantime. (You probably also want to include an increment of the version_number field as an F expression in the update call.) Karen -- You received this message because you are subscribed to the Google Groups "Django users" group. To post to this group, send email to django-us...@googlegroups.com. To unsubscribe from this group, send email to django-users+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/django-users?hl=en.
