I'm trying to atomically increment a simple counter in Django. My code looks like this:
from models import Counter from django.db import transaction @transaction.commit_on_success def increment_counter(name): counter = Counter.objects.get_or_create(name = name) counter.count += 1 counter.save()
If I understand Django correctly, this should wrap the function in a transaction and make the increment atomic. But it doesn't work and there is a race condition in the counter update. How can this code be made thread-safe?
Counter.objects.get_or_create(name = name) Counter.objects.filter(name = name).update(count = F('count')+1)
or using an F expression:
counter = Counter.objects.get_or_create(name = name) counter.count = F('count') +1 counter.save( update_fields=["count"] )
Remember to Specify Which fields to update, Or you might encounter race conditions on other possible fields of the model!
A topic on the race condition associated with this approach has been added to the official documentation.