Django update queryset with annotation

For Django 1.11+ you can use Subquery:

from django.db.models import OuterRef, Subquery, Sum

Relation.objects.update(
    rating=Subquery(
        Relation.objects.filter(
            id=OuterRef('id')
        ).annotate(
            total_rating=Sum('sign_relations__rating')
        ).values('total_rating')[:1]
    )
)

This code produce the same SQL code proposed by Tomasz Jakub Rup but with no use of RawSQL expression. The Django documentation warns against the use of RawSQL due to the possibility of SQL injection).

Update

I published an article based on this answer with more in-depth explanations: Updating a Django queryset with annotation and subquery on paulox.net