Django DateTimeField auto_now_add not working

Question

In one of the model i have set one timestamp field as follows:

created_datetime = models.DateTimeField(auto_now_add = True)

While in shell i am able to create a obj and save it, however in my application it is raising a exception that created_datetime field cannot be null.

Confused where things went wrong!! How to reslove it.

Better use a custom `save()` rather than using `auto_now_add`. [Read this.](http://stackoverflow.com/questions/1737017/django-auto-now-and-auto-now-add) — Konstant, May 05 '11 at 15:07

score 15 · Answer 1 · answered May 05 '11 at 15:21

15

As far as I know, best practice for default datetimes is to use the following:

created_datetime = models.DateTimeField(default=datetime.datetime.now)

Don't forget to import datetime

answered May 05 '11 at 15:21

Alex Jillard

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is there a similar approach for ``auto_now`` or is it fine as-is? – Ben Keating Aug 12 '11 at 21:50
I believe best practice for `auto_now` is overriding `save()` and setting the datetime manually. – Alex Jillard Aug 15 '11 at 17:16
As of 2018, this information is outdated. Best practice according to django is to use auto_now=True. – Anuvab Mohanty Aug 23 '18 at 07:05
I had to use `initial=` instead of `default=` – stefanbschneider Oct 16 '20 at 21:40

score 4 · Answer 2 · answered Jun 22 '18 at 11:02

I had this and it really confused me for ages.

Turned out that my model had a custom primary key, and it was due to a bug not setting it when constructing some test objects.

The first time this worked fine as auto_now_add set created_at. The second time it didn't as the object with a null primary key already existed, so it was doing an update. And it tried to set that to created_at null, which wasn't allowed in my model.

So worth checking if you end up on this question with the error "in my application it is raising a exception that created_datetime field cannot be null", that that could be caused by not setting a primary key correctly.

The solution was for me to correctly set a primary key.

Thanks so much for this comment, it helped me out. My case was that I was reusing a primary key to make a new record, and django/sqlite for some reason didn't say "you cannot reuse that key", instead it complained about the created_at field. Your hint here really saved me a lot of time. — rossdavidh, Apr 08 '20 at 17:29

score 3 · Accepted Answer · answered May 31 '14 at 09:53

3

You can do something like this

created_datetime = models.DateTimeField(auto_now_add=True, auto_now=False)

answered May 31 '14 at 09:53

Ashish

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I don't understand - how and why does that help? – frabcus Jun 20 '18 at 20:02

score 0 · Answer 4 · answered Feb 22 '22 at 12:36

data_obj = Organization.objects.get(id=id)
.....
created_at = data_obj.created_at

It means call your old saved created_at data from database and re-save again during Updation created_at fields not working so save it statically, no need to do dynamically. My model is created_at = models.DateTimeField(auto_now_add=True)

score -2 · Answer 5 · answered Aug 17 '13 at 14:19

-2

The following way is in the "part1" of django documentation

from django.utils import timezone
p = Poll(question="What's new?", pub_date=timezone.now())

answered Aug 17 '13 at 14:19

doyoubi

1

Django DateTimeField auto_now_add not working

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