#33018: Incorrect annotation value when doing a subquery with empty queryset
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Reporter: decomorreno | Owner: nobody
Type: Bug | Status: new
Component: Database layer | Version: 3.2
(models, ORM) |
Severity: Normal | Resolution:
Keywords: orm, annotate, | Triage Stage: Accepted
EmptyQuerySet, empty, count |
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
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Changes (by Simon Charette):
* stage: Unreviewed => Accepted
Comment:
The `0` assignment on empty result set comes from
[https://github.com/django/django/blob/6c3525a09db5177bf4e3856de85bf8b1300402d5/django/db/models/sql/compiler.py#L268-L270
this line]. I assume we could adjust the logic to rely on `getattr(col,
'empty_aggregate_value', NotImplemented)` and fallback to `'0'` if it's
missing.
Makes me wonder if we want to rename `empty_aggregate_value` to
`empty_result_set_value` instead since it's not entirely bound to
aggregation anymore.
e.g. the following should exhibit the same behavior
{{{#!python
Author.objects.annotate(annotation=Coalesce(Author.objects.empty(), 42))
}}}
It also seems weird that we default to `0` as opposed to `NULL` which
would be a more correct value.
Alternatively we could adjust `Coalesce.as_sql` to catch `EmptyResultSet`
when it's compiling its source expressions but that's more involved as
most of the logic for that currently lives in `Func.as_sql`. We could also
use both of these approaches.
--
Ticket URL: <https://code.djangoproject.com/ticket/33018#comment:2>
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