#32879: Using annotate and extra in ORM
-------------------------------------+-------------------------------------
Reporter: Zerq | Owner: nobody
Type: Uncategorized | Status: new
Component: Database layer | Version: 3.2
(models, ORM) |
Severity: Normal | Resolution:
Keywords: QuerySet.extra | 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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Description changed by Zerq:
Old description:
> 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(...)
> }}}
New description:
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(...)
}}}
I file this issue to show usage of extra, as asked in documentation.
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Ticket URL: <https://code.djangoproject.com/ticket/32879#comment:1>
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