Django CharField with dynamic default value

I want to add a new field to a PostgreSQL database.

It's a not null and unique CharField, like

dyn = models.CharField(max_length=50, null=False, unique=True)

The database already has relevant records, so it's not an option to

  • delete the database
  • reset the migrations
  • wipe the data
  • set a default static value.

How to proceed?

you can reset the migrations or edit it or create new one like:

python makemigrations name_you_want

after that:

python migrate same_name

edit: example for funcation:

def generate_default_data():

class MyModel(models.Model):
     field = models.DateTimeField(default=generate_default_data)

I ended up using one of the methods shown by Oleg

def dynamic_default_value():
    This function will be called when a default value is needed.
    It'll return a 31 length string with a-z, 0-9.
    alphabet = string.ascii_lowercase + string.digits
    return ''.join(random.choices(alphabet, k=31)) # 31 is the length of the string


dyn = models.CharField(max_length=31, null=False, unique=True, default=dynamic_default_value)

If the field was max_length of 32 characters then I'd have used the hex_uuid() present in the question.

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