Django update queryset with annotation

Question

I want to update all rows in queryset by using annotated value.

I have a simple models:

class Relation(models.Model):
    rating = models.IntegerField(default=0)

class SignRelation(models.Model):
    relation = models.ForeignKey(Relation, related_name='sign_relations')
    rating = models.IntegerField(default=0)

And I want to awoid this code:

for relation in Relation.objects.annotate(total_rating=Sum('sign_relations__rating')):
    relation.rating = relation.total_rating or 0
    relation.save()

And do update in one SQL-request by using something like this:

Relation.objects.update(rating=Sum('sign_relations__rating'))

Doesn't work:

TypeError: int() argument must be a string or a number, not 'Sum'

or

Relation.objects.annotate(total_rating=Sum('sign_relations__rating')).update(rating=F('total_rating'))

Also doesn't work:

DatabaseError: missing FROM-clause entry for table "relations_signrelation"
LINE 1: UPDATE "relations_relation" SET "rating" = SUM("relations_si...

Is it possible to use Django's ORM for this purpose? There is no info about using update() and annotate() together in docs.