#16649: Models.save() refactoring: check updated rows to determine action
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Reporter: akaariai | Owner: nobody
Type: | Status: closed
Cleanup/optimization | Version: 1.3
Component: Database layer | Resolution: fixed
(models, ORM) | Triage Stage: Ready for
Severity: Normal | checkin
Keywords: | Needs documentation: 0
Has patch: 1 | Patch needs improvement: 0
Needs tests: 0 | UI/UX: 0
Easy pickings: 0 |
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Comment (by akaariai):
While using update_fields on one of my projects I noticed a possible
reason to revert the way update count is used in this ticket's committed
patch. On PostgreSQL, if there is a trigger for the updated table, and
this trigger returns NULL in some conditions, then the UPDATE statement is
seen as affecting zero rows. This will result in Django seeing zero rows
updated, and this again will result in error when using update_fields as
the update didn't seem to affect any rows.
For plain .save() in 1.6 the result will be IntegrityError - the update
doesn't seem to affect any rows, but there is a row matching the update
condition in the DB, so Django will try to UPDATE, see no rows matched,
and then try to INSERT -> boom.
The end result is that code that worked in 1.5 will not work in 1.6 if
there are ON UPDATE triggers which return NULL. I am not sure about how
common this condition will be. It will be easy to change the detection in
save_base() from UPDATE - if not updated - INSERT to SELECT - if found
UPDATE - else INSERT. But I would like to wait and see if this problem is
common enough to worry about...
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Ticket URL: <https://code.djangoproject.com/ticket/16649#comment:12>
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