#24835: exists() incorrect after annotation with Count()
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Reporter: pteromys | Owner: nobody
Type: Bug | Status: new
Component: Database layer (models, ORM) | Version: 1.8
Severity: Normal | Keywords:
Triage Stage: Unreviewed | Has patch: 0
Easy pickings: 0 | UI/UX: 0
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exists() is returning wrong answers when I'm filtering on the results of
Count(). Maybe I wanted to know whether any blog post had gotten over 100
comments. The following transcripts are on Django 1.8.1 / Python 2.7.9 /
SQLite. The answer is also wrong on Python 3.4.3 but correct on Django
1.7.4.
== Testcase (see below for setup) ==
Assume at least 2 Users exist in the database.
{{{
>>> User.objects.annotate(c=models.Count('id')).values_list('c')
[(1,), (1,)]
>>> User.objects.annotate(c=models.Count('id')).filter(c__gt=1)
[]
}}}
So far this is to be expected. No user has more than one id--which makes
the following surprising.
{{{
>>> User.objects.annotate(c=models.Count('id')).filter(c__gt=1).exists()
True
}}}
What further raises the suspicion of unintended behavior is that if you
increase the "1" to the number of Users (or higher), then the exists()
starts to return False.
{{{
>>>
User.objects.annotate(c=models.Count('id')).filter(c__gt=User.objects.count()).exists()
False
}}}
== Setup ==
{{{
$ django-admin2 startproject blah
$ cd blah
$ ./manage.py syncdb
...
You have installed Django's auth system, and don't have any superusers
defined.
Would you like to create one now? (yes/no): no
$ ./manage.py shell
>>> from django.contrib.auth.models import User
>>> User.objects.create(username='a')
>>> User.objects.create(username='b')
>>> from django.db import models
}}}
--
Ticket URL: <https://code.djangoproject.com/ticket/24835>
Django <https://code.djangoproject.com/>
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