id	summary	reporter	owner	description	type	status	component	version	severity	resolution	keywords	cc	stage	has_patch	needs_docs	needs_tests	needs_better_patch	easy	ui_ux
31773	ExpressionWrapper loses output_field for combined expression without an output_field.	Thodoris Sotiropoulos	Mariusz Felisiak	"I have the following model.

{{{#!python
class Mallets(models.Model):
    id = models.AutoField(primary_key=True,blank=True, null=True)
    hindsight = models.ForeignKey(Hindsight, models.DO_NOTHING, blank=True, null=True)
    believer = models.IntegerField(blank=True, null=True)
    damnably = models.IntegerField(blank=True, null=True)
    issue = models.IntegerField(blank=True, null=True)
    glover = models.TextField(blank=True, null=True)  # This field type is a guess.

    class Meta:
        db_table = 'mallets'
}}}

and I perform the following query on Django 3.2

{{{#!python
sheer = ExpressionWrapper((F('issue') / F('id')), output_field=FloatField())
lacquer = ExpressionWrapper(Avg(F('sheer'), output_field=FloatField()), output_field=TextField())
q = Mallets.objects.using('default')
ret = q.annotate(sheer=sheer).values('sheer').annotate(lacquer=Sum(F('believer'))).order_by('sheer').first()
}}}

Django however throws the following exception

{{{
Traceback (most recent call last):
  File ""driver_sqlite.py"", line 25, in <module>
    ret2 = ret1.annotate(sheer=sheer).values('sheer').annotate(lacquer=Sum('believer')).order_by('sheer').first()
  File ""/home/.env/lib/python3.6/site-packages/Django-3.2-py3.6.egg/django/db/models/query.py"", line 678, in first
    for obj in (self if self.ordered else self.order_by('pk'))[:1]:
  File ""/home/.env/lib/python3.6/site-packages/Django-3.2-py3.6.egg/django/db/models/query.py"", line 287, in __iter__
    self._fetch_all()
  File ""/home/.env/lib/python3.6/site-packages/Django-3.2-py3.6.egg/django/db/models/query.py"", line 1305, in _fetch_all
    self._result_cache = list(self._iterable_class(self))
  File ""/home/.env/lib/python3.6/site-packages/Django-3.2-py3.6.egg/django/db/models/query.py"", line 111, in __iter__
    for row in compiler.results_iter(chunked_fetch=self.chunked_fetch, chunk_size=self.chunk_size):
  File ""/home/.env/lib/python3.6/site-packages/Django-3.2-py3.6.egg/django/db/models/sql/compiler.py"", line 1113, in results_iter
    results = self.execute_sql(MULTI, chunked_fetch=chunked_fetch, chunk_size=chunk_size)
  File ""/home/.env/lib/python3.6/site-packages/Django-3.2-py3.6.egg/django/db/models/sql/compiler.py"", line 1148, in execute_sql
    sql, params = self.as_sql()
  File ""/home/.env/lib/python3.6/site-packages/Django-3.2-py3.6.egg/django/db/models/sql/compiler.py"", line 498, in as_sql
    extra_select, order_by, group_by = self.pre_sql_setup()
  File ""/home/.env/lib/python3.6/site-packages/Django-3.2-py3.6.egg/django/db/models/sql/compiler.py"", line 60, in pre_sql_setup
    group_by = self.get_group_by(self.select + extra_select, order_by)
  File ""/home/.env/lib/python3.6/site-packages/Django-3.2-py3.6.egg/django/db/models/sql/compiler.py"", line 142, in get_group_by
    sql, params = expr.select_format(self, sql, params)
  File ""/home/.env/lib/python3.6/site-packages/Django-3.2-py3.6.egg/django/db/models/expressions.py"", line 388, in select_format
    if hasattr(self.output_field, 'select_format'):
  File ""/home/.env/lib/python3.6/site-packages/Django-3.2-py3.6.egg/django/utils/functional.py"", line 48, in __get__
    res = instance.__dict__[self.name] = self.func(instance)
  File ""/home/.env/lib/python3.6/site-packages/Django-3.2-py3.6.egg/django/db/models/expressions.py"", line 269, in output_field
    output_field = self._resolve_output_field()
  File ""/home/.env/lib/python3.6/site-packages/Django-3.2-py3.6.egg/django/db/models/expressions.py"", line 309, in _resolve_output_field
    source.__class__.__name__,
django.core.exceptions.FieldError: Expression contains mixed types: IntegerField, AutoField. You must set output_field.
}}}

Note that when I run the query above on Django 3.0.8, this query runs as expected. So is this a regression in Django 3.2?"	Bug	closed	Database layer (models, ORM)	3.1	Release blocker	fixed			Ready for checkin	1	0	0	0	0	0