Django: Using an F expression for a text field in an update call

Question

In a django view, I need to append string data to the end of an existing text column in my database. So, for example, say I have a table named \"ATable\", and it has a fiel

Answer 1

You can use the Concat db function.

from django.db.models import Value
from django.db.models.functions import Concat

ATable.objects.filter(id=100).update(some_field=Concat('some_field', Value('more string')))

In my case, I am adding a suffix for facebook avatars URIs like this:

FACEBOOK_URI = 'graph.facebook.com'
FACEBOOK_LARGE = '?type=large'
# ...
users = User.objects.filter(Q(avatar_uri__icontains=FACEBOOK_URI) & ~Q(avatar_uri__icontains=FACEBOOK_LARGE))
users.update(avatar_uri=Concat('avatar_uri', Value(FACEBOOK_LARGE)))

and I get SQL like this (Django 1.9):

UPDATE `user_user` SET `avatar_uri` = CONCAT(COALESCE(`user_user`.`avatar_uri`, ''), COALESCE('?type=large', ''))
WHERE (`user_user`.`avatar_uri` LIKE '%graph.facebook.com%' AND NOT (`user_user`.`avatar_uri` LIKE '%?type=large%' AND `user_user`.`avatar_uri` IS NOT NULL))

The result is all image URIs were changed from http://graph.facebook.com//picture to http://graph.facebook.com//picture?type=large