Making queries using F() and timedelta at django

Question

I have the following model:

class Process(models.Model):
  title = models.Charfield(max_length=255)
  date_up = models.DateTimeField(auto_now_add=True)
  day         


        

Answer 1

7 days == 1 day * 7

F is deep-black Django magic and the objects that encounter it must belong to the appropriate magical circles to handle it.

In your case, django.db.models.query.filter knows about F, but datetime.timedelta does not. Therefore, you need to keep the F out of the timedelta argument list. Fortunately, multiplication of timedelta * int is supported by F, so the following can work:

Process.objects.filter(date_up__lte=datetime.now()-timedelta(days=1)*F('days_activation'))

As it turns out, this will work with PostgreSQL, but will not work with SQlite (for which Django 1.11 only supports + and - for timedelta, perhaps because of a corresponding SQlite limitation).