Django migrations changing choices value - mysql

Question

A field has been added to one of my MySQL table previously:
# -*- coding: utf-8 -*-
# Generated by Django 1.9.7 on 2017-09-14 00:49
from __future__ import unicode_literals
from django.db import migrations, models
class Migration(migrations.Migration):
dependencies = [
('my_app', '0102_previous_migrations'),
]
operations = [
migrations.AddField(
model_name='my_client',
name='my_team',
field=models.CharField(choices=[('Unassigned', 'Unassigned'), ('ACT', 'ACT'), ('Korea', 'Korea'), ('National', 'National')], default='Unassigned', max_length=255, verbose_name='My Team'),
),
]
So users have a choices of the above selection in my UI and will be saved into the table my_client:
Unassigned
ACT
Korea
National
The changes have been deployed and now a beginner like me would like to change, i.e. remove Korea and add 2 new choices: NSW and SA
How would I go about this? Do I need another migration or I will just need to change those choices in the models?
I use this in my model now like this:
class Client(MyAppModel):
TEAM_CHOICES = (
('Unassigned', 'Unassigned'),
('ACT', 'ACT'),
('Korea', 'Korea'),
('National', 'National'),
)
DEFAULT_TEAM = 'Unassigned'
my_team = models.CharField(verbose_name='MyTeam', null=False, max_length=255, choices=TEAM_CHOICES, default=DEFAULT_TEAM)
Update:
Base on the comment I have, I will need a migration too, a AlterField?
Do I also have to update all the existing value right now in the table my_client if any of them is having Korea to say Unassigned if I would like to remove Korea as a choice? What command can I use in the migration?

Answer 1

A high-level approach:
Create a migration which only adds the new choice. Write a method to take all models with the old choice, and give them a proper new choice migration.RunPython. Create a migration which removes the old choice.

Answer 2

Figure this out later, hope it helps others beginner like me.
I have to update the Client model
class Client(MyAppModel):
TEAM_CHOICES = (
('Unassigned', 'Unassigned'),
('National', 'National'),
('NSW', 'NSW'),
('SA', 'SA'),
)
Then enter this command:
python manage.py makemigrations
A migration will be generated:
from __future__ import unicode_literals
from django.db import migrations, models
class Migration(migrations.Migration):
dependencies = [
('my_app', '0102_previous_migrations'),
]
operations = [
migrations.AlterField(
model_name='my_client',
name='my_team',
field=models.CharField(choices=[('Unassigned', 'Unassigned'), ('ACT', 'ACT'), ('National', 'National'), ('NSW', 'NSW'), ('SA', 'SA')], default='Unassigned', max_length=255, verbose_name='My Team'),
),
]
Next to update all the existing values in the table now, referred here, enter this command to create an empty migration file:
python manage.py makemigrations --empty my_app
In the new migration file, put something like:
# -*- coding: utf-8 -*-
# Generated by Django 1.9.7 on 2017-10-26 06:36
from __future__ import unicode_literals
from django.db import migrations
def set_unassigned(apps, schema_editor):
Client = apps.get_model('my_app', 'my_client')
for client in Client.objects.all():
client.account_team = 'Unassigned'
client.save()
class Migration(migrations.Migration):
dependencies = [
('my_app', '0104_client_team_update'),
]
operations = [
migrations.RunPython(set_unassigned),
]