How to add a default array of values to ArrayField?

Question

Is it possible to add a default value to ArrayField?

I tried to do this for email field, but this did not work:

constants.py:

ORDER_STATUS_CHANGED = 'order_status_changed'
NEW_SIGNAL = 'new_signal'

NOTIFICATION_SOURCE = (
    (ORDER_STATUS_CHANGED, 'Order Status Changed'),
    (NEW_SIGNAL, 'New Signal'),

)

models.py:

from notifications import constants
from django.contrib.postgres.fields import ArrayField

class NotificationSetting(models.Model):
    user = models.OneToOneField(User, on_delete=models.CASCADE, primary_key=True, related_name='notification_setting')

    telegram = ArrayField(models.CharField(
        choices= constants.NOTIFICATION_SOURCE,
        max_length=30
    ), default=list)

    email = ArrayField(models.CharField(
        choices= constants.NOTIFICATION_SOURCE,
        max_length=16
    ), default=list(dict(constants.NOTIFICATION_SOURCE).keys()))

    class Meta:
        db_table = 'notification_settings'

    def __str__(self):
        return f'Notification setting for user {self.user}'

And override the save method of the model would be bad practice, I think.

The problem is that in the django admin site I see that the default values did not count when the object was created. (UPD. Maibe i have problem with my custom ChoiseArrayField widged)

And i get this mesagge: WARNINGS: notifications.NotificationSetting.email: (postgres.E003) ArrayField default should be a callable instead of an instance so that it's not shared between all field instances. HINT: Use a callable instead, e.g., uselistinstead of[]``

Can you also post the error you receive and how the constants look like? — Darius Bogdan
– Darius Bogdan, Commented Mar 20, 2020 at 18:18
update post. >Can you also post the error you receive I don't recieve a error. Only warning about default: ArrayField default should be a callable instead of an instance so that it's not shared between all field instances. HINT: Use a callable instead, e.g., use list instead of [] The problem is that in the django admin site I see that the default values did not get out — PrefixEt
– PrefixEt, Commented Mar 22, 2020 at 9:37

Darius Bogdan · Accepted Answer · 2020-03-22 09:55:04Z

The default property on an ArrayField should be a callable. You can read more about that here: https://docs.djangoproject.com/en/3.0/ref/contrib/postgres/fields/.

What you are getting by placing directly there list(dict(constants.NOTIFICATION_SOURCE).keys()) is just a warning so it should still add the defaults to the field. By placing this default directly there it will put in the migrations the following thing and the values will be shared across all field instances:

default=['order_status_changed', 'new_signal']

To get rid of the warning you should create a function that returns the default value:

def get_email_default():
    return list(dict(constants.NOTIFICATION_SOURCE).keys())

and put the function as the default to the field:

email = ArrayField(models.CharField(
    choices= constants.NOTIFICATION_SOURCE,
    max_length=16
), default=get_email_default)

By doing this the warning will be gone and from the function you can have logic for choosing the default value.

After doing this, in the migrations the default value will look like this:

default=my_model.models.get_email_default

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