#32879: Using annotate and extra in ORM
-------------------------------------+-------------------------------------
Reporter: Zerq | Owner: nobody
Type: | Status: new
Uncategorized |
Component: Database | Version: 3.2
layer (models, ORM) |
Severity: Normal | Keywords: QuerySet.extra
Triage Stage: | Has patch: 0
Unreviewed |
Needs documentation: 0 | Needs tests: 0
Patch needs improvement: 0 | Easy pickings: 0
UI/UX: 0 |
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In simple example:
{{{
class Foo(models.Model):
pass
class Bar(models.Model):
baz = models.ForeignKey('Foo', on_delete=models.PROTECT)
}}}
I want to count reverse relation count and then select_for_update:
{{{
Foo.objects.annotate(Count('bar')).select_for_update().get(...)
}}}
but this does not work: django.db.utils.NotSupportedError: FOR UPDATE is
not allowed with GROUP BY clause
To circumvent this problem I used:
{{{
Foo.extra(select={'bar_count': 'SELECT COUNT(*) FROM "app_bar" U0 WHERE
U0."baz_id" = "app_foo"."id"'}).select_for_update().get(...)
}}}
--
Ticket URL: <https://code.djangoproject.com/ticket/32879>
Django <https://code.djangoproject.com/>
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