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#32007 closed Bug (fixed)

QuerySet.annotate() with WhereNode() crashes with AttributeError.

Reported by:	Gordon Wrigley	Owned by:	Mariusz Felisiak
Component:	Database layer (models, ORM)	Version:	3.1
Severity:	Release blocker	Keywords:
Cc:		Triage Stage:	Accepted
Has patch:	yes	Needs documentation:	no
Needs tests:	no	Patch needs improvement:	no
Easy pickings:	no	UI/UX:	no

Description

I think I've found a regression in 3.1, I'm seeing this across databases and Python versions but only on Django 3.1.
With reference to the polls app the queryset I hit this on is essentially:

Question.objects.values("question_text").annotate(
    pub_date__count=Count("pub_date", distinct=True),
    pub_date__is_null=ExpressionWrapper(Q(pub_date=None), output_field=BooleanField())
).values("question_text", "pub_date__count", "pub_date__is_null")

This results in:

~\.venv\django_tutorial\lib\site-packages\django\db\models\query.py in annotate(self, *args, **kwargs)
   1121                     clone.query.group_by = True
   1122                 else:
-> 1123                     clone.query.set_group_by()
   1124                 break
   1125

~\.venv\django_tutorial\lib\site-packages\django\db\models\sql\query.py in set_group_by(self, allow_aliases)
   1979                     if not allow_aliases or alias in column_names:
   1980                         alias = None
-> 1981                     group_by_cols = annotation.get_group_by_cols(alias=alias)
   1982                 group_by.extend(group_by_cols)
   1983         self.group_by = tuple(group_by)

~\.venv\django_tutorial\lib\site-packages\django\db\models\expressions.py in get_group_by_cols(self, alias)
    867
    868     def get_group_by_cols(self, alias=None):
--> 869         expression = self.expression.copy()
    870         expression.output_field = self.output_field
    871         return expression.get_group_by_cols(alias=alias)

AttributeError: 'WhereNode' object has no attribute 'copy'

It's a bit of a dumb query but given my usecase https://pypi.org/project/django-data-browser/ that's a little beyond my control.

Still it's kinda surprising that it worked on 3.0 and doesn't on 3.1.

It can be simplified a bit and still get essentially the same result:

Question.objects.annotate(
    pub_date__count=Count("pub_date", distinct=True),
    pub_date__is_null=ExpressionWrapper(Q(pub_date=None), output_field=BooleanField())
)

Removing either of the annotate clauses "fixes" it.

Change History (11)

comment:1 by Mariusz Felisiak, 4 years ago

Component:	Uncategorized → Database layer (models, ORM)
Severity:	Normal → Release blocker
Summary:	AttributeError: 'WhereNode' object has no attribute 'copy' → QuerySet.annotate() with WhereNode() crashes with AttributeError.
Triage Stage:	Unreviewed → Accepted
Type:	Uncategorized → Bug

Thanks for the report.

Regression in 8a6df55f2dd5131282084a4edfd48f63fbf8c69a.
Reproduced at bcc2befd0e9c1885e45b46d0b0bcdc11def8b249.

comment:2 by Simon Charette, 4 years ago

The best way of resolving this is likely to add a WhereNode.copy method.

comment:3 by Gordon Wrigley, 4 years ago

Here is a more useful variant, this is a type thing I actually do on a regular basis, and I guess also means work won't be upgrading to 3.1 until I find a work around.

Question.objects.annotate(
    pub_date__is_null=ExpressionWrapper(Q(pub_date=None), output_field=BooleanField())
).values("pub_date__is_null").annotate(
    id__count=Count("id", distinct=True)
).values("pub_date__is_null", "id__count")