I have an object of type Foo with a ForeignKey to a Bar. Bar has a property called slug.
I can do
myfoo.bar = Bar.objects.get(slug='123')
But this would add an extra query. Is it possible to have Django generate the assignment as a sub-query within the update?
i.e. generate SQL similar to:
UPDATE myfoo SET bar_id = (select id from bar where slug = '123')
You can use a Django Subquery expression:
from django.db.models import Subquery
# create the "SELECT id FROM bar WHERE slug = '123' LIMIT 1" subquery
subquery = Bar.objects.filter(slug='123')[:1]
# update only the correct foo object with this subquery
Foo.objects.filter(pk=myfoo.pk).update(bar=Subquery(subquery))
# refresh the variable so that `myfoo.bar` is correct
myfoo.refresh_from_db()