How to make a random entry value in a Django model?

Question

Django

I have a user model where
chars = 'abcdefghijklmnopqrstuvwxyz0123456789'
code = get_random_string(32, chars)
...
ref_code = models.CharField(default=code, unique=True)
Since users already exist, a
django.db.utils.IntegrityError occurs : (1062, "Duplicate entry '4krrtv4eacbn0lw6sii88gkedqm7xn45' for key 'ref_code'")
It's understandable, it tries to give all users the same "random" string.
How to avoid this on an already existing user model?

Answer 1

ref_code = models.CharField(default=lambda: get_random_string(32, chars), unique=True)

In general, what did uuid not please?

Answer 2

remove uniq and default, make null=True, do migration to create field, then do datamigration to populate all fields randomly, then add uniq and default and do migration again