#34251: Paginator should warn if ordering is not deterministic
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Reporter: Alexandr Tatarinov | Owner: nobody
Type: New feature | Status: new
Component: Core (Other) | Version: 4.1
Severity: Normal | Keywords:
Triage Stage: Unreviewed | Has patch: 0
Needs documentation: 0 | Needs tests: 0
Patch needs improvement: 0 | Easy pickings: 0
UI/UX: 0 |
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As documented in tickets #28657 and #28261, at least some database
backends will produce non-deterministic ordering when sorting by columns
with non-unique values.
This leads to inconsistent pagination, which I argue falls under the same
category as paginating by unordered QuerySet. To make things worse, this
one is easy to overlook, since non-unique columns like "name" can have
mostly unique values and you need to have duplicates at the page borders
to observe the issue, so it's more likely to happen in production
environments after operating fine for quite a while.
I suggest we add a warning similar to the UnorderedObjectListWarning when
total ordering as defined
[https://github.com/django/django/blob/main/django/contrib/admin/views/main.py#L390
in admin changelist] is not specified.
The outstanding question is, how to realistically deal with this situation
when ordering is provided by the end-user? It's typical to have i.e. "sort
by price asc/desc" option in the UI or API, which will result in a warning
since the price is not a unique column. Pushing responsibility to add "pk"
to each sorting option to the front end does not seem like a reasonable
way to me. This may be out of the scope of the current ticket, but I want
to make sure we have a plan. I would say we also shouldn't insert pk
automatically like ChangeList does, it'll at least break indexing as in
this ticket #29943. Would like to hear your thoughts.
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Ticket URL: <https://code.djangoproject.com/ticket/34251>
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