#32433: Delete distinct produces an unexpected and potentially harmful SQL
-------------------------------------+-------------------------------------
Reporter: egism | Owner: nobody
Type: Bug | Status: new
Component: Database layer | Version: 3.1
(models, ORM) |
Severity: Normal | Resolution:
Keywords: orm, delete, | Triage Stage: Accepted
distinct |
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
-------------------------------------+-------------------------------------
Changes (by Simon Charette):
* keywords: orm, delete, distinct, postgresql => orm, delete, distinct
* type: Uncategorized => Bug
* stage: Unreviewed => Accepted
Comment:
I think we should start by failing loudly when `distinct().delete()` is
used as adding support for it would require a subquery pushdown (`DELETE
FROM table WHERE field IN (SELECT DISTINCT field FROM table`) which would
require a non negligible amount of work and additional complexity for the
rare cases where this is useful and a manual `__in` subquery lookup can be
used to achieve the same results e.g.
{{{#!python
Comment.objects.filter(
post_id__in=Comment.objects.order_by('post_id',
'created_at').distinct('post_id').values('post_id')
).delete()
}}}
**egism** if you want to work on a patch you should raise a `TypeError` in
`QuerySet.delete` if `self.query.distinct or self.query.distinct_fields`.
A regression test can then be added to `delete_regress/tests`
([https://github.com/django/django/blob/5fcfe5361e5b8c9738b1ee4c1e9a6f293a7dda40/tests/delete_regress/tests.py
source]).
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Ticket URL: <https://code.djangoproject.com/ticket/32433#comment:2>
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