Django can't auto save DateTimeFields

Question

Hi I have a model like so:

from datetime import datetime


class Project(models.Model):
    created = models.DateTimeField(editable=False)
    updated = models.DateTimeField(editable=False)
    product = models.ForeignKey('tool.product')
    module = models.ForeignKey('tool.module')
    model = models.ForeignKey('tool.model')
    zipcode = models.IntegerField(max_length=5)

    def save(self, **kwargs):
        if not self.id:
            self.created = datetime.now()
        self.updated = datetime.now()
        super(Project, self).save()

    def __unicode__(self):
        return self.id

However when I try to save a project I get:

coercing to Unicode: need string or buffer, long found

and from the runserver:

RuntimeWarning: DateTimeField received a naive datetime (2012-10-31 14:45:36.611622) while time zone support is active.

I'm not sure exactly what the problem is here but I'm assuming it has something to do with timezone getting in the way of saving the DateTimeField.

Any help would be much appreciated.

I'm just wondering... is there any reason why you are not using auto_now and auto_now_add available for [DateField and DateTimeField](https://docs.djangoproject.com/en/dev/ref/models/fields/#datefield) — César, Oct 31 '12 at 19:55
I read that it was not a very good implementation: http://www.benspaulding.us/weblog/2008/aug/02/auto_now_add-evil/, http://stackoverflow.com/questions/1737017/django-auto-now-and-auto-now-add — Darwin Tech, Oct 31 '12 at 19:58

rantanplan · Accepted Answer · 2012-10-31T20:34:59.103

4

First of all DateTimeField supports auto updating like this:

created = models.DateTimeField(editable=False, auto_now_add=True) # Only on creation
updated = models.DateTimeField(editable=False, auto_now=True)     # On every save

Secondly the RuntimeWarning you get, means that you have enabled in your settings.py timezone aware datetime objects e.g you will see the following:

USE_TZ = True

When you do that, you have to treat datetime objects differently, you have to pass explicitly a tzinfo value.

# install the `pytz` module through pip or whatnot
from pytz import timezone
import datetime
from django.utils.timezone import utc

now = datetime.datetime.utcnow().replace(tzinfo=utc)

# To show the time in Greece
athens = timezone('Europe/Athens')
print now.astimezone(athens)

For more info see the django docs and the pytz docs.

About the coercing to Unicode: error, try doing this:

def __unicode__(self):
    return unicode(self.id)

edited Oct 31 '12 at 20:34

answered Oct 31 '12 at 19:55

rantanplan

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Is there some way to enable TZ as well as auto saving? – Darwin Tech Oct 31 '12 at 19:59
Or is there a problem if I have TZ disabled? – Darwin Tech Oct 31 '12 at 20:03
What I'm saying is that if you look at your settings.py then USE_TZ will be True. But when you do your thing with the datetime objects, you don't use timezones. That's why django is nagging you. – rantanplan Oct 31 '12 at 20:03
@DarwinTech It depends on what you want to do. I always use timezone aware dates. I ll update my post. – rantanplan Oct 31 '12 at 20:04
So I changed the model to `auto_save` but I am still getting the unicode error. – Darwin Tech Oct 31 '12 at 20:37
@DarwinTech Look at the bottom of the answer. I just updated. – rantanplan Oct 31 '12 at 20:37

score 0 · Answer 2 · answered Mar 04 '14 at 06:22

What I did to store now on creation, was use the default attribute of the DateTimeField, and Django's now() wrapper like so:

from django.utils import timezone

ctime = models.DateTimeField(default=timezone.now)

Please note that this date is in UTC timezone, if you require some other time zone to be set, wrap timezone.now in a lambda that calls localtime()

Django can't auto save DateTimeFields

2 Answers2