#30325: Inconsistent count() behaviour on reverse relations in ManyToManyFields
with custom model manager
-------------------------------------+-------------------------------------
Reporter: Tobias | Owner: nobody
Kunze |
Type: Bug | Status: new
Component: Database | Version: 2.2
layer (models, ORM) |
Severity: Normal | Keywords:
Triage Stage: | Has patch: 0
Unreviewed |
Needs documentation: 0 | Needs tests: 0
Patch needs improvement: 0 | Easy pickings: 0
UI/UX: 0 |
-------------------------------------+-------------------------------------
When looking up a reverse relation on a ManyToManyField that uses a custom
model manager, not using `all()` before calling `count()` will not use the
custom model manager. This results in `obj.m2m_lookup.count()` yielding a
different result than `obj.m2m_lookup.all().count`, which is new behaviour
in 2.2, and unexpected (at least to me).
I've written up a [https://github.com/rixx/django-22-issue minimal test
case] to showcase the issue. Inlining here:
{{{
#!python
from django.db import models
class Author(models.Model):
name = models.CharField(max_length=100)
class BookManager(models.Manager):
def get_queryset(self):
return super().get_queryset().exclude(state='deleted')
class Book(models.Model):
title = models.CharField(max_length=100)
authors = models.ManyToManyField(to=Author, related_name='books')
state = models.CharField(choices=(('regular', 'regular'), ('deleted',
'deleted')), default='regular', max_length=100)
objects = BookManager()
a = Author.objects.create(name='Bill')
b1 = Book.objects.create(title='Sonnets', state='deleted')
b2 = Book.objects.create(title='Hamlet')
b1.authors.add(a)
b2.authors.add(a)
a.books.count() # Returns 2
a.books.all().count() # Returns 1
}}}
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Ticket URL: <https://code.djangoproject.com/ticket/30325>
Django <https://code.djangoproject.com/>
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