#34462: Deletions in admin panel create N + 1 queries
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Reporter: Mike Lissner | Owner: nobody
Type: Cleanup/optimization | Status: new
Component: contrib.admin | Version: 3.2
Severity: Normal | Resolution:
Keywords: performance | Triage Stage: Accepted
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 1 | UI/UX: 0
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Changes (by Simon Charette):
* stage: Unreviewed => Accepted
Comment:
In order to solve this issue we'd have to introduce a new
`ModelAdmin.log_deletions` method as `log_deletion` only allows a single
object to be passed which would require adding a
`LogEntryManager.log_actions` method. If we're going forward with this
change we should also make something for the changelist form view that
relies on `log_addition` and `log_change`. Any bypass of `log_deletion`
and friends for newly introduced bulk logging methods should be documented
in release notes and we should also possibly keep calling into the old
method for a deprecation period if they are overridden in subclasses.
The `delete_selected` action
[https://github.com/django/django/blob/38e63c9e61152682f3ff982c85a73793ab6d3267/django/contrib/admin/actions.py#L46-L57
has another issue that go beyond the one reported here]. It issues a
`count()` query and then issues a follow up query that retrieve each
objects which ultimately makes `count()` unnecessary since `len(queryset)`
can be used to reduce the number of queries but more importantly
[https://github.com/django/django/blob/38e63c9e61152682f3ff982c85a73793ab6d3267/django/contrib/admin/actions.py#L55
to report the accurate number of deleted objects].
[https://docs.djangoproject.com/en/4.2/topics/db/optimization/#don-t
-overuse-contains-count-and-exists It's even a documented anti-pattern in
our docs].
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Ticket URL: <https://code.djangoproject.com/ticket/34462#comment:1>
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