#34067: django.core.Paginator wrong query slicing
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Reporter: Hristo Trendafilov | Owner: nobody
Type: Bug | Status: closed
Component: Core (Other) | Version: 3.2
Severity: Normal | Resolution: needsinfo
Keywords: | Triage Stage:
Paginator,slice,queryset | Unreviewed
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
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Changes (by Mariusz Felisiak):
* status: new => closed
* resolution: => needsinfo
Comment:
> It is Django fault for those reasons:
>
> * `order_by` might be complicated but is supported by the framework
> * Chained `order_by` is also supported
Yes, but you should be aware what you are using in the `ORDER BY` clause
and that some fields may cause issues, e.g. multi-valued fields (see
[https://docs.djangoproject.com/en/stable/ref/models/querysets/#order-by
notes in docs]). Django cannot decide for you.
> * queryset slicing is a feature of Django queryset API.
> * queryset slicing should act like list and string slicing and namely to
provide you with results `[ from : to ]` indexes provided and not to
change or lose data in between. Or in other words - what is passed in the
`Paginator.object_list` should be just sliced `[ from : to ]`. `Paginator`
should never care for the queryset, what is the ordering of the queryset,
what is excluded and so on - it should just work with it.
This would require fetching all results and slicing on the Python side not
in the database which is very ineffective and would cause many performance
issues.
> * changing `paginate_by` to `10` or greater fixes the problem.
`paginate_by` is a standard and documented Django ListView setting.
> * changing `order_by` to some other `order_by` also fixes the problem.
`order_by` should work the same or if any limitations those should be well
documented
Limitations are mostly documented, but we cannot document all caveats.
> P.S. That is also happening in Django 2.2
Django 2.2 is not supported anymore, and Django 3.2 is in extended support
so it receives only security patches.
I understand that you spend a lot of time trying to debug your issue, but
we don't have your app, your data, and your database, so we're unable to
help. Also, Trac is not a support channel.
I'd like to highly recommend using one of
[https://code.djangoproject.com/wiki/TicketClosingReasons/UseSupportChannels
support channel] where folks will help you. If you'll still be convinced
that Django is at fault, then please attach a sample minimal project that
reproduces the issue.
--
Ticket URL: <https://code.djangoproject.com/ticket/34067#comment:9>
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