#26600: map says a queryset is not iterable
-------------------------------------+-------------------------------------
Reporter: ihucos | Owner: nobody
Type: Bug | Status: closed
Component: Database layer | Version: 1.11
(models, ORM) |
Severity: Normal | Resolution: wontfix
Keywords: queryset iterator | Triage Stage:
map | Unreviewed
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
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Comment (by Philipp Kuznetsov):
I'm really sorry, of course in case of `in` exception message is `argument
of type 'QuerySet' is not iterable`. This has nothing to do with `map` and
ofc there's an obvious workaround with `exists()`. What I am afraid of is
if there are more of this hidden cases where queryset's `__iter__` raises
an exception and it's shadowed by the outer code exception.
Replying to [comment:11 Simon Charette]:
> Philipp, if you hit a similar exception that means `map` must be
involved somehow.
>
> If you didn't call it yourself then it's likely caused by a usage of
`map` internally in the queryset iteration code.
>
> In this case the ticket resolution still stands, Python 2 `map`'s
shadowing of the underlying exception makes it impossible to determine its
true nature and thus we cannot conclude Django is at fault. As mentioned
previously this should all be solved on Python 3 where `map` doesn't
exhibit this behaviour.
>
> By the way an `in` operation on a queryset you are disposing off is
likely to trigger a `MemoryError` just like in the original report. I'd
suggest you opt for something along
`queryset.filter(pk=instance.pk).exists()` instead.
--
Ticket URL: <https://code.djangoproject.com/ticket/26600#comment:12>
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