Opened 5 years ago

Last modified 2 years ago

#30655 closed Bug

len(queryset) and queryset.count() return different results — at Initial Version

Reported by: Sander Kleijwegt Owned by: nobody
Component: Database layer (models, ORM) Version: dev
Severity: Normal Keywords:
Cc: Triage Stage: Unreviewed
Has patch: no Needs documentation: no
Needs tests: no Patch needs improvement: no
Easy pickings: no UI/UX: no

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 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)>]>

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