#22550: QuerySet last() and reverse() confusing when used with ordered slices
-------------------------------------+-------------------------------------
Reporter: jdufresne | Owner: merll
Type: Bug | Status: assigned
Component: Database layer | Version: 1.6
(models, ORM) | Resolution:
Severity: Normal | Triage Stage: Accepted
Keywords: | Needs documentation: 0
Has patch: 1 | Patch needs improvement: 0
Needs tests: 0 | UI/UX: 0
Easy pickings: 0 |
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Changes (by merll):
* has_patch: 0 => 1
Comment:
A PR has been sent, which fixes the behavior as described in ticket 22550.
It also includes an addition to the docs, describing that sorting and
filtering are not possible after the slicing operation:
https://github.com/django/django/pull/2677
'''Note:''' It is potentially breaking backwards compatibility in
`QuerySet.last()` and `QuerySet.reverse()`. Using `reverse()` and `last()`
on querysets was programmatically possible even after they had been
sliced, provided that
* models have defined `ordering`,
* no further filters or sorting was used.
Although it has never delivered correct nor consistent results, these two
functions may have been used under aforementioned conditions. After
applying this patch, this will raise an error. In this process, the test
for ticket 7235 had to be revised, as it was relying on the wrong order of
operations.
--
Ticket URL: <https://code.djangoproject.com/ticket/22550#comment:3>
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