#30542: Float-valued aggregations and annotations with filters fail with
AttributeError
-------------------------------------+-------------------------------------
Reporter: Chuan- | Owner: nobody
Zheng Lee |
Type: Bug | Status: new
Component: Database | Version: 2.2
layer (models, ORM) | Keywords: aggregation,
Severity: Normal | annotation, filter
Triage Stage: | Has patch: 0
Unreviewed |
Needs documentation: 0 | Needs tests: 0
Patch needs improvement: 0 | Easy pickings: 0
UI/UX: 0 |
-------------------------------------+-------------------------------------
When any float-valued aggregation or annotation (`Avg`, `StdDev`,
`Variance`) is used with the `filter=` keyword argument, the following
exception is raised:
{{{
AttributeError: 'WhereNode' object has no attribute 'output_field'
}}}
For example, these queries all fail with this error:
{{{#!python
Speaker.objects.annotate(average=Avg('speakerscore__score',
filter=Q(speakerscore__ghost=False)))
Speaker.objects.annotate(average=StdDev('speakerscore__score',
filter=Q(speakerscore__ghost=False)))
Team.objects.annotate(average=Avg('debateteam__teamscore__score',
filter=Q(debateteam__teamscore__forfeit=False)))
}}}
The error seems to be raised irrespective of what's in the database
(''e.g.'', it's raised even for an empty database). However, it doesn't
affect aggregations like `Sum`, `Max` or `Min` that don't use
`NumericOutputFieldMixin`. Also, queries that don't use the `filter=`
keyword in the aggregation work fine.
The exception in question is raised from line 46 of
django/db/models/functions/mixins.py, which looks for an `output_field`
attribute of every element of `self.get_source_expressions()`, where
`self` is the object containing `NumericOutputFieldMixin`, in this case
`Avg` or some other subclass of `Aggregate`. But
`Aggregate.get_source_expressions()` includes `self.filter` in its list,
and (post-compilation) `self.filter` is a `WhereNode`, which doesn't have
an `output_field` attribute.
This issue is new in version 2.2. Everything works fine in version 2.1
(where I believe `NumericOutputFieldMixin` didn't exist, or at least
wasn't on the MRO for `Avg`, `StdDev` or `Variance`).
=== Minimal reproducible example
In a blank (or any) project, insert in models.py:
{{{#!python
from django.db.models import Model, FloatField, BooleanField
class Book(Model):
price = FloatField()
fiction = BooleanField()
}}}
then run migrations and in `python manage.py shell`:
{{{
$ python manage.py shell
Python 3.6.7 (default, Oct 22 2018, 11:32:17)
[GCC 8.2.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
(InteractiveConsole)
>>> from django22_output_field_bug.models import Book
>>> from django.db.models import Avg, Q
>>> Book.objects.annotate(average=Avg('price', filter=Q(fiction=True)))
Traceback (most recent call last):
[...]
File "/[...]/django/db/models/functions/mixins.py", line 46, in
<genexpr>
if any(isinstance(s.output_field, DecimalField) for s in
source_expressions):
AttributeError: 'WhereNode' object has no attribute 'output_field'
>>> Book.objects.aggregate(average=Avg('price', filter=Q(fiction=True)))
Traceback (most recent call last):
[...]
File "/[...]/django/db/models/functions/mixins.py", line 46, in
<genexpr>
if any(isinstance(s.output_field, DecimalField) for s in
source_expressions):
AttributeError: 'WhereNode' object has no attribute 'output_field'
}}}
--
Ticket URL: <https://code.djangoproject.com/ticket/30542>
Django <https://code.djangoproject.com/>
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