[Answered ]-Django: Avoiding ABA scenario in Database and ORM’s

If this is purely an arithmetic expression then Django has a nice API called F expressions

Updating attributes based on existing fields

Sometimes you’ll need to perform a simple arithmetic task on a field, such as incrementing or decrementing the current value. The obvious way to achieve this is to do something like:

>>> product = Product.objects.get(name='Venezuelan Beaver Cheese')
>>> product.number_sold += 1
>>> product.save()

If the old number_sold value retrieved from the database was 10, then the value of 11 will be written back to the database.

This can be optimized slightly by expressing the update relative to the original field value, rather than as an explicit assignment of a new value. Django provides F() expressions as a way of performing this kind of relative update. Using F() expressions, the previous example would be expressed as:

>>> from django.db.models import F
>>> product = Product.objects.get(name='Venezuelan Beaver Cheese')
>>> product.number_sold = F('number_sold') + 1
>>> product.save()

This approach doesn’t use the initial value from the database. Instead, it makes the database do the update based on whatever value is current at the time that the save() is executed.

Once the object has been saved, you must reload the object in order to access the actual value that was applied to the updated field:

>>> product = Products.objects.get(pk=product.pk)
>>> print product.number_sold
42