#27554: Queryset evaluation fails with mix of nested and flattened prefetches
(AttributeError on RelatedManager)
-------------------------------------+-------------------------------------
Reporter: Anthony Leontiev | Owner: nobody
Type: Bug | Status: new
Component: Database layer | Version: 1.10
(models, ORM) |
Severity: Normal | Resolution:
Keywords: prefetch | Triage Stage: Accepted
AttributeError prefetch_related |
nested RelatedManager |
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
-------------------------------------+-------------------------------------
Comment (by Vimarsh Chaturvedi):
Hey guys,
My first time posting here.
I tried reproducing the bug, and was able to.
I added the following cases as per Simon Charette's suggestion and Django
didn't throw any exception.
views.py
{{{
#Code in orinigal test project by Anthony Leontiev
def setup():
a = A.objects.create()
b = B.objects.create()
b.a = a
b.save()
d = D.objects.create()
C.objects.create(b=b, d=d)
#Succeeded: As reported above.
def nested_prefetch(request, *args, **kwargs):
setup()
queryset = A.objects.all().prefetch_related(
Prefetch(
'b',
queryset=B.objects.all().prefetch_related(
Prefetch(
'c',
queryset=C.objects.all().prefetch_related(
'd'
)
)
)
)
)
content = queryset[0].b.c.all()[0].d.pk
return HttpResponse(content)
#Failed: As reported above.
def flat_prefetch(request, *args, **kwargs):
setup()
queryset = A.objects.all().prefetch_related(
Prefetch(
'b',
queryset=B.objects.all().prefetch_related(
Prefetch('c__d')
)
)
)
content = queryset[0].b.c.all()[0].d.pk
return HttpResponse(content)
#The following three cases were added by me
#Failed: As expected.
def flat_prefetch_one(request, *args, **kwargs):
setup()
queryset = A.objects.all().prefetch_related(
Prefetch(
'b',
queryset=B.objects.all().prefetch_related('c__d')
)
)
content = queryset[0].b.c.all()[0].d.pk
return HttpResponse(content)
#Succeeded: I was expecting this and the following case to fail too, but
they didn't.
def flat_prefetch_two(request, *args, **kwargs):
setup()
queryset = A.objects.all().prefetch_related(
Prefetch('b__c__d')
)
content = queryset[0].b.c.all()[0].d.pk
return HttpResponse(content)
#succeeded
def flat_prefetch_three(request, *args, **kwargs):
setup()
queryset = A.objects.all().prefetch_related('b__c__d')
content = queryset[0].b.c.all()[0].d.pk
return HttpResponse(content)
}}}
--
Ticket URL: <https://code.djangoproject.com/ticket/27554#comment:3>
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