#33414: Diamond inheritance causes duplicated PK error when creating an object,
if
the primary key field has a default.
-------------------------------------+-------------------------------------
Reporter: Yu Li | Owner: Yu Li
Type: Bug | Status: assigned
Component: Database layer | Version: 4.0
(models, ORM) |
Severity: Normal | Resolution:
Keywords: | Triage Stage: Accepted
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
-------------------------------------+-------------------------------------
Comment (by Simon Charette):
Thank you for your detailed report.
I haven't looked into the details of how this can be addressed but one
thing is certain. When an instance of model class at the ''head'' of a
diamond inheritance graph is saved the ORM knows that there isn't a reason
to update involved tables/nodes more than once. In other words, creating a
`BookReview` should only require 4 queries and not 6 and this issue
predates babd4126853e48594b61e8db71a83d7bdd929b9c. I believe that's what
we should focus on solving here as that will address this unfortunate
collision while reducing the number of queries to a minimum.
Test coverage for model diamond inheritance is limited given it's a rarely
used feature and ''good'' core support for fields with Python generated
defaults is also relatively recent so I'm not surprised we missed this
relatively obscure edge case in #29129.
--
Ticket URL: <https://code.djangoproject.com/ticket/33414#comment:5>
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