On Fri, 2014-12-05 at 00:21 -0800, Peter Geoghegan wrote: > On Thu, Dec 4, 2014 at 10:27 PM, Anssi Kääriäinen > <anssi.kaariai...@thl.fi> wrote: > > For Django's use case this is a requirement. We must inform the user if > > the save() action created a new row or if it modified an existing one. > > Can you explain that in more detail, please?
Django has a post_save signal. The signal provide information of the save operation. One piece of information is a created boolean flag. When set to True the operation was an insert, on False it was an update. See https://docs.djangoproject.com/en/1.7/ref/signals/#django.db.models.signals.post_save for details. The created flag is typically used to perform some related action. An example is User and UserProfile models. Each user must have an UserProfile, so post_save can be used to create an empty userprofile on creation of user. If Django is going to use the INSERT ... ON CONFLICT UPDATE variant in Django for the existing save() method, then it needs to know if the result was an UPDATE or INSERT. If we are going to use this for other operations (for example bulk merge of rows to the database), it would be very convenient to have per-row updated/created information available so that we can fire the post_save signals for the rows. If we don't have that information available, it means we can't fire signals, and no signals means we can't use the bulk merge operation internally as we have to fire the signals where that happened before. Outside of Django there are likely similar reasons to want to know if the result of an operation was a creation of a new row. The reason could be creation of related row, doing some action in application layer, or just UI message telling "object created successfully" vs "object updated successfully". - Anssi -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
