#25937: Failure when using expressions.DateTime on NULL values and aggregating
----------------------------------------------+---------------------------
Reporter: trecouvr | Owner: nobody
Type: Bug | Status: new
Component: Database layer (models, ORM) | Version: 1.9
Severity: Normal | Keywords: orm aggregate
Triage Stage: Unreviewed | Has patch: 0
Easy pickings: 0 | UI/UX: 0
----------------------------------------------+---------------------------
Running query like `qs.annotate(time=DateTime('removed'), 'month',
timezone.UTC()).values('time').annotate(Count('pk'))` fails with
`<repr(<gill.contrib.sales.models.TransactionRowQuerySet at 0x10cc99320>)
failed: ValueError: Database returned an invalid value in
QuerySet.datetimes(). Are time zone definitions for your database and pytz
installed?>`. I noted the failure on MySQL and PostgreSQL, Django 1.8.X
and 1.9.X. I did not try on other db backends or other Django versions.
To reproduce the behaviour:
1. create a model:
{{{
class Potato(models.Model):
..
removed = models.DateTimeField(null=True, blank=True)
}}}
2. Insert some of them
{{{
Potato.objects.create(removed=timezone.now())
Potato.objects.create(removed=None)
..
}}}
3. Fire the request
{{{
# Failure
Potato.annotate(time=DateTime('removed'), 'month',
timezone.UTC()).values('time').annotate(c=Count('pk'))
# Success
Potato.filter(removed__isnull=False).annotate(time=DateTime('removed'),
'month', timezone.UTC()).values('time').annotate(c=Count('pk'))
}}}
Note: I printed the raw sql generated by Django and fired it directly in a
db shell without any error, so the problem seems to come from the code
Django uses to convert the result from the backend to python code,
especially the line with NULL coming from the aggregation:
{{{
+---------------------+-----------+
| time | pk__count |
+---------------------+-----------+
| NULL | 17 |
| 2015-01-01 00:00:00 | 7 |
..
}}}
--
Ticket URL: <https://code.djangoproject.com/ticket/25937>
Django <https://code.djangoproject.com/>
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