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
31919	Django fails with FieldError: Expression contains mixed types: IntegerField, AutoField. You must set output_field.	StefanosChaliasos	Simon Charette	"I have the following query.


{{{
expr = Value(3) * F('id')                                                  
o = Model.objects.using('default')                                         
res = o.values('field_name').annotate(expr=expr).values('expr')
print(res)
}}}

Unfortunately, this query crashes with a FieldError exception. The track trace is


{{{
Traceback (most recent call last):
  File ""example.py"", line 28, in <module>
    print(res)
  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 1316, 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 1115, 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 1147, 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 55, in pre_sql_setup
    self.setup_query()
  File ""/home/.env/lib/python3.6/site-packages/Django-3.2-py3.6.egg/django/db/models/sql/compiler.py"", line 46, in setup_query
    self.select, self.klass_info, self.annotation_col_map = self.get_select()
  File ""/home/.env/lib/python3.6/site-packages/Django-3.2-py3.6.egg/django/db/models/sql/compiler.py"", line 267, in get_select
    sql, params = col.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 385, 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 266, 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 463, in _resolve_output_field
    return super()._resolve_output_field()
  File ""/home/.env/lib/python3.6/site-packages/Django-3.2-py3.6.egg/django/db/models/expressions.py"", line 306, in _resolve_output_field
    source.__class__.__name__,
django.core.exceptions.FieldError: Expression contains mixed types: IntegerField, AutoField. You must set output_field.
}}}

This should be a regression bug because the previous query works in Django 3.1
"	Bug	closed	Database layer (models, ORM)	dev	Release blocker	fixed		Matt Hegarty	Ready for checkin	1	0	0	0	0	0