Objects count after Many to many related query shows wrong

[noufalvlpr]

class Standard(models.Model):
    name = models.CharField(max_length=30)
    created_at = models.DateField(null=True, blank=True)


class Product(models.Model):
    name = models.CharField(max_length=30, null=True)
    standards = models.ManyToManyField(Standard, related_name='products')

created standards with created_at=Null, added some standards to product and after

Product.objects.count()  # 6
Product.objects.filter(standards__created_at__isnull=True).count()  # 7

[Carlton Gibson]

Hi.

created standards with created_at=Null, added some standards to product and after

This is too vague to allow us to reproduce the issue.

Can you please provide the exact steps needed to recreate to issue, preferably in a test case or script.

This is core ORM behaviour: it's highly unlikely to be a bug. It's possible of course but, it's much more likely to be something in you code, which you've not specified here.

If you can provide a reproduce example we can investigate.

[noufalvlpr]

I am afraid may be its my mistake ..

Steps to reproduce this issue

s1 = Standard.objects.create(name='standard1')
s2 = Standard.objects.create(name='standard2')
p1 = Product.objects.create(name='product1')
p1.standards.add(s1)
p1.standards.add(s2)

Product.objects.count() # 1
Product.objects.filter(standards__created_at__isnull=True).count() # 2

[Tim Graham]

To get the correct count, you need to use ​QuerySet.distinct() since the query is joined to a many-to-many table.