#26426: Use case for QuerySet.extra: annotate query with the existence of a
relation
--------------------------------+--------------------------------------
Reporter: yourcelf | Owner: nobody
Type: Uncategorized | Status: new
Component: Uncategorized | Version: 1.9
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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Changes (by AlexHill):
* needs_better_patch: => 0
* needs_tests: => 0
* needs_docs: => 0
Comment:
It's not a great deal better, it is possible using RawSQL in an annotation
rather than extra:
{{{
from django.db.models.expressions import RawSQL
exists_sql = """EXISTS (
SELECT "id" FROM "extra_category_followers"
WHERE "extra_category_followers"."category_id"="extra_category"."id"
AND "extra_category_followers"."user_id"=%s
)"""
Category.objects.all().annotate(is_following=RawSQL(exists_sql,
(request.user.id,)))
}}}
--
Ticket URL: <https://code.djangoproject.com/ticket/26426#comment:1>
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