Question

I get a model object, change an attribute, save it and it still has the old attribute:

>>> g = SiteProfile.objects.get(pk=3)
>>> g.renew_date
datetime.date(2010, 4, 11)
>>> g.renew_date = date.today()+timedelta(days=365)
>>> g.renew_date
datetime.date(2011, 4, 11)
>>> g.save()
>>> g.renew_date
datetime.datetime(2010, 4, 11, 16, 57, 4, 192684)

Anyone know if this is an issue with the database or something else?

Answer 1

I figured it out.

The issue was that the field renew_date had the argument auto_now set to True as such:

renew_date = models.DateField(auto_now=True, editable=False)

I understood auto_now to mean that the current date will be used when creating the object, but it turns out that’s not the case:

DateField.auto_now

Automatically set
the field to now every time the object
is saved. Useful for “last-modified”
timestamps. Note that the current date
is always used; it’s not just a
default value that you can override.

From django docs.

What I needed was auto_now_add which:

Automatically set the field to now
when the object is first created.
Useful for creation of timestamps.
Note that the current date is always
used; it’s not just a default value
that you can override.

So, after changing my renew_date field:

renew_date = models.DateField(auto_now_add=True, editable=False)

it all works, just fine 🙂

>>> g = SelectStatProfile.objects.get(pk=3)
>>> g.renew_date
datetime.date(2010, 4, 11)
>>> from datetime import date, timedelta
>>> g.renew_date = date.today()+timedelta(days=365)
>>> g.renew_date
datetime.date(2011, 4, 11)
>>> g.save()
>>> g.renew_date
datetime.date(2011, 4, 11)