Migrate charfield's choice in django

migration.py

# If you change some field's choice, django will not migrate the value at
# the database level. You need to do it.
#
# Generate an empty migration:
# > python manage.py makemigrations --empty <app_name>
#
# This will migration the value in the `state` field from `new` to `new_b` 
# (and back if necessary).

from django.db import migrations



class Migration(migrations.Migration):
    dependencies = [("<app_name>", "0001_abc")]

    operations = [
        migrations.RunSQL(
            "update <app_name>_<table> set state='new_b' where state='new';",
            "update <app_name>_<table> set state='new' where state='new_b';",
        )
    ]