After resetting uwsgi, the default=datetime.now() in Django models consistently saves the exact same datetime

I encountered an issue with my model code that involved datetime settings:

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

Upon migrating and restarting uwsgi, I noticed that the first datetime entry in MariaDB was correct, but all subsequent entries were identical to the initial one after resetting uwsgi.

2015-04-19 16:01:46
2015-04-19 16:01:46
2015-04-19 16:01:46
2015-04-19 16:01:46

To address this issue, I made a change to the code as follows:

added_time = models.DateTimeField(
    auto_now_add=True
)

Although this adjustment resolved the problem, I'm still unsure of why this behavior occurred in the first place.

pythondjangodatetimeuwsgi

Answer №1

default=datetime.datetime.now() is calculated when the model is parsed/compiled and remains unchanged afterwards. To calculate now() at the time of adding/updating an object, you should use:

default=datetime.datetime.now, which assigns now as a callable function. Django will execute it during runtime.

Using auto_now_add is also a valid solution (though subtly different -- providing a default value will update it each time the model is saved, while auto_now_add only does it once, upon creation).

Do not worry, this error is a very common oversight.

Answer №2

Make sure to pass in datetime.datetime.now instead of datetime.datetime.now() as the default value. This way, the default value is calculated only when needed and not always on model initialization, ensuring you get a different value after each restart.

For a more detailed explanation, refer to the Django documentation.

If you are using Django's time zones support, be sure to utilize django.utils.timezone.now instead of datetime.datetime.now.

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