#30655: len(queryset) and queryset.count() return different results
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Reporter: Sander Kleijwegt | Owner: nobody
Type: Bug | Status: new
Component: Uncategorized | Version: 2.2
Severity: Normal | Resolution:
Keywords: | Triage Stage: 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 Sander Kleijwegt):
* version: 2.0 => 2.2
Old description:
> According to the queryset.count() documentation "you should always use
> count() rather than loading all of the record into Python objects and
> calling len() on the result" (see
> [https://docs.djangoproject.com/en/2.0/ref/models/querysets/#count
> here]), which seems to imply that the results of both functions should
> always be identical. Here is a simple example that shows the contrary.
>
> Models:
> {{{
> class Bar(models.Model):
> pass
>
> class Foo(models.Model):
> fooint = models.IntegerField()
> foobar = models.ForeignKey(Bar, related_name='foos',
> on_delete=models.CASCADE)
> }}}
>
> Shell Output:
> {{{
> >>> import django
> >>> django.__version__
> '2.0.4'
> >>> from foobar.models import Foo, Bar
> >>> bar = Bar.objects.create()
> >>> foo1 = Foo.objects.create(fooint=1, foobar=bar)
> >>> foo2 = Foo.objects.create(fooint=2, foobar=bar)
> >>> Bar.objects.all().order_by('foos__fooint').count()
> 1
> >>> len(Bar.objects.all().order_by('foos__fooint'))
> 2
> >>> Bar.objects.all().order_by('foos__fooint')
> <QuerySet [<Bar: Bar object (1)>, <Bar: Bar object (1)>]>
> }}}
New description:
According to the queryset.count() documentation "you should always use
count() rather than loading all of the record into Python objects and
calling len() on the result" (see
[https://docs.djangoproject.com/en/2.0/ref/models/querysets/#count here]),
which seems to imply that the results of both functions should always be
identical. Here is a simple example that shows the contrary.
Models:
{{{
class Bar(models.Model):
pass
class Foo(models.Model):
fooint = models.IntegerField()
foobar = models.ForeignKey(Bar, related_name='foos',
on_delete=models.CASCADE)
}}}
Shell Output:
{{{
>>> import django
>>> django.__version__
'2.2.3'
>>> from foobar.models import Foo, Bar
>>> bar = Bar.objects.create()
>>> foo1 = Foo.objects.create(fooint=1, foobar=bar)
>>> foo2 = Foo.objects.create(fooint=2, foobar=bar)
>>> Bar.objects.all().order_by('foos__fooint').count()
1
>>> len(Bar.objects.all().order_by('foos__fooint'))
2
>>> Bar.objects.all().order_by('foos__fooint')
<QuerySet [<Bar: Bar object (1)>, <Bar: Bar object (1)>]>
}}}
--
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Ticket URL: <https://code.djangoproject.com/ticket/30655#comment:1>
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