[Django]-Adding days to a date via the ORM

Unfortunatelly, you can’t do that with F expressions: https://code.djangoproject.com/ticket/16487

You can either write a custom sql query using the .raw() method, or you can use standard filters to get this to work, but only if all your models have the same days_due value, which is probably not the case – but just in case, you can do it like this:

Item.objects.filter(issue_date__lte=now - datetime.timedelta(days=days))

I think you can’t do this in a db agnostic way. I would use an extra(select) to add a is_due field to your query. Something like (not tested):

Item.objects.extra(select={'is_due': 'issue_date + days_due'})

could work on a postgres database. Put the extra select in a custom manager to isolate the database specific code.