Combining Q objects with empty querysets crashes.

[Bogumil Schube]

Working example with django 4.0

from django.db import models
from django.db.models import Q

class Test(models.Model):
   pass

out = Test.objects.none()
for a, b in [(1,1),(2,2),(3,3)]:
   out |= Q(a=a, b=b)

> out
> Out[23]: <Q: (OR: (AND: ('a', 1), ('b', 1)), (AND: ('a', 2), ('b', 2)), (AND: ('a', 3), ('b', 3)))>

In django 4.1 it's resulting in an AttributeError

site-packages/django/db/models/query.py:1951, in QuerySet._check_operator_queryset(self, other, operator_)
   1950 def _check_operator_queryset(self, other, operator_):
-> 1951     if self.query.combinator or other.query.combinator:
   1952         raise TypeError(f"Cannot use {operator_} operator with combined queryset.")

AttributeError: 'Q' object has no attribute 'query'

This error (or feature?) seems to come from #33127

[Mariusz Felisiak]

Thanks for the report. As far as I'm aware combining querysets (empty or not) with Q() objects have never been officially supported, documented, or tests. This worked for empty querysets in Django 4.0, but accidentally and only due to the order of EmptyQuerySet guards. You should use Q() as the starting point for building dynamically Q objects, e.g.:

out = Q()
for a, b in [(1,1),(2,2),(3,3)]:
   out |= Q(a=a, b=b)

[Bogumil Schube]

Thanks for explaining and the solution.