#34067: django.core.Paginator wrong query slicing
-------------------------------------+-------------------------------------
Reporter: Hristo | Owner: nobody
Trendafilov |
Type: Bug | Status: new
Component: Core | Version: 3.2
(Other) | Keywords:
Severity: Normal | Paginator,slice,queryset
Triage Stage: | Has patch: 0
Unreviewed |
Needs documentation: 0 | Needs tests: 0
Patch needs improvement: 0 | Easy pickings: 0
UI/UX: 0 |
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A have a ListView defined like so:
{{{
class AllPracticesListView(LoginRequiredMixin, PermissionRequiredMixin,
ListView, ToolBoxFunctions):
template_name = 'practice_list.html'
model = Practice
paginate_by = 6
permission_required = 'customauth.access_practices'
def get_queryset(self):
qs = self.get_all_practices_by_user().order_by(
'company_branch__pk',
'practice_profile__personal_profile__last_name').prefetch_related('practice_profile')
# method < get_all_practices_by_user > is a toolbox method that
returns:
#
Practice.objects.filter(company_branch__owner=self.request.user).order_by('pk')
return qs
}}}
Models are defined like so:
{{{
class Practice(models.Model):
company_branch = models.ForeignKey(
CompanyBranch,
on_delete=models.PROTECT,
related_name='practices',
)
# CompanyBranch model has an owner field which ForeignKey
to the user model
practice_profile = models.ForeignKey(
PracticeProfile,
on_delete=models.PROTECT,
related_name='practices',
)
class PracticeProfile(models.Model):
personal_profile = models.ForeignKey(
PersonalProfile,
on_delete=models.PROTECT,
blank=True,
null=True,
)
# PersonalProfile model has a field called < last_name
>
}}}
Or schematically:
{{{
Practice object relations:
-> CompanyBranch
-> PracticeProfile
-> PersonalProfile /*NULLABLE RELATION/
}}}
When the code is run, the view does not display results correctly.
I did like so to get the WRONG result:
Added a breakpoint on {{{Paginator._get_page}}} return statement
Queryset is passed okay and is available in
{{{Paginator.object_list}}}
But in the args of {{{Paginator._get_page}}} the queryset is totally
different than expected / should be a slice from the first six elements of
{{{Paginator.object_list}}} /
I have tried to add a breakpoint like so
[[Image(https://imgur.com/SdaQUt6)]]
Then I get this result [[Image(https://imgur.com/5zzLNV0)]].
As you can see, PKs 1632, 1624, etc. are missing, objects are
different/marked red and purple/, and are actually removed and never shown
in the view.
If you run slice manually at this point - everything is again fine
[[Image(https://imgur.com/yvn8KMO)]]
This happens only on NULL PersonalProfile objects.
I did like so to get OKAY results:
1. Added a simple breakpoint is added on {{{Paginator.page}}} like so
[[Image(https://imgur.com/d7J5BMZ)]] and that breakpoint is just run then
the result is okay [[Image(https://imgur.com/ILDHAMN)]]
2. changed paginate_by to 10
3. changed {{{order_by}}} in {{{get_queryset}}} to {{{-pk}}}
4. call again the {{{page = paginator.page(page_number)}}}
--
Ticket URL: <https://code.djangoproject.com/ticket/34067>
Django <https://code.djangoproject.com/>
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