Django F expressions joined field

Question

So I am trying to update my model by running the following:

FooBar.objects.filter(something=True).update(foobar=F('foo__bar')) 

but I get the following error:

FieldError: Joined field references are not permitted in this query 

if this is not allowed with F expressions...how can I achieve this update?

ticket

given the information in this ticket, I now understand that this is impossible and will never be implemented in django, but is there any way to achieve this update? maybe with some work around? I do not want to use a loop because there are over 10 million FooBar objects, so SQL is much faster than python.

Answer 1

Django 1.11 adds supports for subqueries. You should be able to do:

from django.db.models import Subquery, OuterRef  FooBar.objects.filter(something=True).update(     foobar=Subquery(FooBar.objects.filter(pk=OuterRef('pk')).values('foo__bar')[:1]) ) 

Answer 2

Why don't use raw sql here: Based on this, it will be something like

from django.db import connection  raw_query = ''' update app_foobar set app_foobar.foobar =  (select app_foo.bar from app_foo where app_foo.id = app_foobar.foo_id)  where app_foobar.something = 1;  '''  cursor = connection.cursor() cursor.execute(raw_query)