Atomic operations in Django?
As of Django 1.1 you can use the ORM's F() expressions.
from django.db.models import Fproduct = Product.objects.get(name='Venezuelan Beaver Cheese')product.number_sold = F('number_sold') + 1product.save()For more details see the documentation:
https://docs.djangoproject.com/en/1.8/ref/models/expressions/#django.db.models.F
If you truly want the counter to be accurate you could use a transaction but the amount of concurrency required will really drag your application and database down under any significant load. Instead think of going with a more messaging style approach and just keep dumping count records into a table for each visit where you'd want to increment the counter. Then when you want the total number of visits do a count on the visits table. You could also have a background process that ran any number of times a day that would sum the visits and then store that in the parent table. To save on space it would also delete any records from the child visits table that it summed up. You'll cut down on your concurrency costs a huge amount if you don't have multiple agents vying for the same resources (the counter).
You can use patch from http://code.djangoproject.com/ticket/2705 for support database level locking.
With patch this code will be atomic:
visitors = VisitorDayTypeCounter.objects.get(day=curday).for_update()visitors.counter += 1visitors.save()