Re: [Django] #14011: QuerySet.none().values('x').query causes "DatabaseError: subquery has too many columns" when used in filters.
#14011: QuerySet.none().values('x').query causes "DatabaseError: subquery has
too
many columns" when used in filters.
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Reporter: skatei | Owner:
Status: new | Milestone:
Component: ORM aggregation | Version: 1.2
Resolution: | Keywords: none
query DatabaseError
Stage: Accepted | Has_patch: 0
Needs_docs: 0| Needs_tests: 0
Needs_better_patch: 0|
--+-
Changes (by mk):
* stage: Unreviewed => Accepted
Comment:
Here's a test for this issue. The failure is still present in trunk.
--
Ticket URL:
Django
Re: [Django] #14011: QuerySet.none().values('x').query causes "DatabaseError: subquery has too many columns" when used in filters.
#14011: QuerySet.none().values('x').query causes "DatabaseError: subquery has
too
many columns" when used in filters.
--+-
Reporter: skatei | Owner:
Status: new | Milestone:
Component: ORM aggregation | Version: 1.2
Resolution: | Keywords: none
query DatabaseError
Stage: Unreviewed | Has_patch: 0
Needs_docs: 0| Needs_tests: 0
Needs_better_patch: 0|
--+-
Changes (by lrekucki):
* needs_better_patch: => 0
* needs_tests: => 0
* needs_docs: => 0
Comment:
This particular error is caused by how EmptyQuerySet handles values().
{{{
>>> print DummyModel.objects.values('pk').none().query
SELECT "simple_dummymodel"."id" FROM "simple_dummymodel"
>>> print DummyModel.objects.none().values('pk').query
SELECT "simple_dummymodel"."id", "simple_dummymodel"."string",
"simple_dummymodel"."text" FROM "simple_dummymodel"
}}}
The returned QuerySet yields wrong SQL which includes additional columns.
This is not a problem, because EmptyQuerySets aren't executed, they just
return empty list as their value. The following code should work properly
(I'm not entirely sure why this won't execute a query, but it works):
{{{
pks = Test.objects.none().values('pk')
print Test.objects.exclude(pk__in=pks)
}}}
I guess the first issue could be fixed, but it wouldn't change the fact
that {{{.query}}} of the EmptyQuerySet doesn't reflect it's result:
{{{
>>> print
DummyModel.objects.filter(pk__in=DummyModel.objects.values('pk').none().query)
[] # should always be []
}}}
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Ticket URL:
Django
[Django] #14011: QuerySet.none().values('x').query causes "DatabaseError: subquery has too many columns" when used in filters.
#14011: QuerySet.none().values('x').query causes "DatabaseError: subquery has
too
many columns" when used in filters.
-+--
Reporter: skatei | Status: new
Milestone: | Component: ORM aggregation
Version: 1.2 |Keywords: none query
DatabaseError
Stage: Unreviewed | Has_patch: 0
-+--
Just came across this error.
{{{
class Test(models.Model):
name = models.CharField(max_length=20)
test = Test(name='bob')
test.save()
pks = Test.objects.none().values('pk').query
print Test.objects.exclude(pk__in=pks)
DatabaseError: subquery has too many columns
}}}
The query:
{{{
SELECT
"error_test"."id",
"error_test"."name",
FROM
"error_test"
WHERE
NOT (
"error_test"."id"
IN (
SELECT
"error_test"."id",
"error_test"."name",
FROM
"error_test"
)
)
}}}
Fixes?:
* Substitute with {{{.filter(pk__in=[])}}} (possibly overriding none).
* Catch and deal with the exception.
* Don't let this happen in the code.
This should at least raise a more meaningful exception if deemed
incorrect.
Reason i'd like it to work is because I apply filters dynamically, using
some complex logic that sometimes applies a none filter.
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Ticket URL:
Django
