Cannot resolve keyword "CAST" in group_by clause.

[user0007]

Hello,

during migrating from Django 1.7.5 to 1.8 I found a bug(?)

truncate_date = connection.ops.date_trunc_sql('day', 'created_at')

qs = MyModel.objects.filter(user_id=1).annotate(max_date=models.Max('created_at')).extra({'created_at': truncate_date}).values('product_id','created_at','max_date')
qs.query.group_by = ['product_id', truncate_date]
qs.order_by('-max_date')[:10]

Traceback (most recent call last):

File "<console>", line 1, in <module>
File "/home/env/local/lib/python2.7/site-packages/django/db/models/query.py", line 138, in repr

data = list(self[:REPR_OUTPUT_SIZE + 1])

File "/home/env/local/lib/python2.7/site-packages/django/db/models/query.py", line 162, in iter

self._fetch_all()

File "/home/env/local/lib/python2.7/site-packages/django/db/models/query.py", line 965, in _fetch_all

self._result_cache = list(self.iterator())

File "/home/env/local/lib/python2.7/site-packages/django/db/models/query.py", line 1085, in iterator

for row in self.query.get_compiler(self.db).results_iter():

File "/home/env/local/lib/python2.7/site-packages/django/db/models/sql/compiler.py", line 783, in results_iter

results = self.execute_sql(MULTI)

File "/home/env/local/lib/python2.7/site-packages/django/db/models/sql/compiler.py", line 818, in execute_sql

sql, params = self.as_sql()

File "/home/env/local/lib/python2.7/site-packages/django/db/models/sql/compiler.py", line 367, in as_sql

extra_select, order_by, group_by = self.pre_sql_setup()

File "/home/env/local/lib/python2.7/site-packages/django/db/models/sql/compiler.py", line 51, in pre_sql_setup

group_by = self.get_group_by(self.select + extra_select, order_by)

File "/home/env/local/lib/python2.7/site-packages/django/db/models/sql/compiler.py", line 102, in get_group_by

expressions.append(self.query.resolve_ref(expr))

File "/home/env/local/lib/python2.7/site-packages/django/db/models/sql/query.py", line 1522, in resolve_ref

self.get_initial_alias(), reuse)

File "/home/env/local/lib/python2.7/site-packages/django/db/models/sql/query.py", line 1461, in setup_joins

names, opts, allow_many, fail_on_missing=True)

File "/home/env/local/lib/python2.7/site-packages/django/db/models/sql/query.py", line 1386, in names_to_path

"Choices are: %s" % (name, ", ".join(available)))

FieldError: Cannot resolve keyword u"CAST(DATE_FORMAT(created_at, '%%Y-%%m-%%d 00:00:00') AS DATETIME)" into field.

This code works perfectly on Django 1.7.5