#34699: Filtering on annotated TruncSecond expression gives unexpected result.
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Reporter: StefanCardnell | Owner: nobody
Type: Uncategorized | Status: new
Component: Uncategorized | Version: 4.2
Severity: Normal | Keywords:
Triage Stage: Unreviewed | Has patch: 0
Needs documentation: 0 | Needs tests: 0
Patch needs improvement: 0 | Easy pickings: 0
UI/UX: 0 |
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With a non-UTC time zone:
{{{#!python
TIME_ZONE = 'Europe/Berlin'
}}}
and a simply query like so
{{{#!python
from django.db.models.functions import TruncSecond
from django.utils import timezone
book = Book.objects.get(id=2)
now = timezone.now()
book.published = now
book.save()
Book.objects.annotate(_published_trunc=TruncSecond('published')).filter(id=2,
_published_trunc__lte=now)
}}}
The result is empty; I have simply filtered `now` against a second-trunced
version of `now` so I would expect a result.
However under the hood the `_published_now` column is converted to a naive
timestamp using `AT TIME ZONE 'Europe/Berlin'` and is thus a naive
timestamp 2 hours ''ahead'' of UTC.
{{{#!sql
SELECT "book"."id",
"book"."published",
DATE_TRUNC('second', "book"."published" AT TIME ZONE
'Europe/Berlin') AS "_published_trunc"
FROM "book"
WHERE ("book"."id" = 2 AND
DATE_TRUNC('second', "book"."_published_trunc" AT TIME ZONE
'Europe/Berlin') <=
'2023-07-04 11:59:00+02:00'::timestamptz)
}}}
The filter compares a naive timestamp to an aware one, but assumes the LHS
naive timestamp is a UTC timestamp - which it is not, it is Berlin time.
**Workaround**
1) Use `TruncSecond(now)` in the filter so the compared naive timestamps
are the same.
2) Use `_published_trunc=TruncSecond('published',
tzinfo=datetime.timezone.utc)` - I don't like this though. It's not clear
without a comment why the tzinfo is needed ''and'' it assumes the database
will compare timezones using UTC.
--
Ticket URL: <https://code.djangoproject.com/ticket/34699>
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