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

Answer 1

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.