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
24142	extra() field overwritten when using union on two querysets	dryice	nobody	"Here's how to reproduce it:

- follow step 1 and step 2 of the tutorial to make the Question and Choice model

- fill in the DB with data:

polls_question;
||= id =||= question_text =||= pub_date =||
|| 1||111||2015-01-13 06:05:58 ||
|| 2||222||2015-01-13 06:06:09 ||
|| 3||333||2015-01-13 06:06:17 ||

polls_choice;
|| id =||= choice_text =||= votes =||= question_id =||
|| 1||1aa||3||1 ||
|| 2||1bb||8||1 ||
|| 3||2aa||9||2 ||
|| 4||2bb||3||2 ||
|| 5||3aa||4||3 ||
|| 6||3bb||2||3 ||

- in the Django shell:
{{{
>>> qs = Question.objects.all()
>>> qs1 = qs.filter(choice__votes__gte=5).annotate(choice_count=Count('choice'))
>>> for i in qs1:
...     print i, i.choice_count
...
111 1
222 1
>>> qs2 = qs.exclude(id__in=qs1.values_list(""id"", flat=True)).extra(select={'choice_count': '1-1'})
>>> for i in qs2:
...     print i, i.choice_count
...
333 0
>>> for i in qs1 | qs2:
...     print i, i.choice_count
...
111 1
222 1
333 2
}}}

Note in the last line, I would expect
{{{333 0}}}
while it gives {{{333 2}}}

Checking the SQL used:
{{{
>>> qs3 = qs1 | qs2
>>> print qs1.query
SELECT ""polls_question"".""id"", ""polls_question"".""question_text"", ""polls_question"".""pub_date"", COUNT(""polls_choice"".""id"") AS ""choice_count"" FROM ""polls_question"" INNER JOIN ""polls_choice"" ON ( ""polls_question"".""id"" = ""polls_choice"".""question_id"" ) WHERE ""polls_choice"".""votes"" >= 5 GROUP BY ""polls_question"".""id"", ""polls_question"".""question_text"", ""polls_question"".""pub_date""

>>> print qs2.query
SELECT (1-1) AS ""choice_count"", ""polls_question"".""id"", ""polls_question"".""question_text"", ""polls_question"".""pub_date"" FROM ""polls_question"" WHERE NOT (""polls_question"".""id"" IN (SELECT U0.""id"" FROM ""polls_question"" U0 INNER JOIN ""polls_choice"" U1 ON ( U0.""id"" = U1.""question_id"" ) WHERE U1.""votes"" >= 5 GROUP BY U0.""id"", U0.""question_text"", U0.""pub_date""))

>>> print qs3.query
SELECT (1-1) AS ""choice_count"", ""polls_question"".""id"", ""polls_question"".""question_text"", ""polls_question"".""pub_date"", COUNT(""polls_choice"".""id"") AS choice_count FROM ""polls_question"" LEFT OUTER JOIN ""polls_choice"" ON ( ""polls_question"".""id"" = ""polls_choice"".""question_id"" ) WHERE (""polls_choice"".""votes"" >= 5 OR NOT (""polls_question"".""id"" IN (SELECT U0.""id"" FROM ""polls_question"" U0 INNER JOIN ""polls_choice"" U1 ON ( U0.""id"" = U1.""question_id"" ) WHERE U1.""votes"" >= 5 GROUP BY U0.""id"", U0.""question_text"", U0.""pub_date""))) GROUP BY ""polls_question"".""id"", ""polls_question"".""question_text"", ""polls_question"".""pub_date"", (1-1)
}}}

It looks the ""|"" operator didn't check if there's extra field with the
same name on the two sides, and
{{{COUNT(""polls_choice"".""id"") AS choice_count}}}
overwrote
{{{SELECT (1-1) AS ""choice_count""}}}

I understand once we started using extra() we are on the edge. But
maybe this is something that could be fixed? Thanks!"	Bug	closed	Database layer (models, ORM)	1.7	Normal	wontfix	QuerySet.extra		Accepted	0	0	0	0	0	0