Run python Django example

To customize nullable previously set to null.

models.py

import uuid


class MyEntity(Model):
    name = CharField(max_length=100, unique=True)
    code = CharField(
        max_length=100,
        unique=True,
        null=True,
        blank=True,
    )

    def save(self, *args, **kwargs):
        if not self.code:
            self.code = f"{self.name}_{uuid.uuid4()}"
        return super().save(*args, **kwargs)

And now to apply this change to existing data, you can create a custom migration.

0002_custom_migration.py

from django.db import migrations, models


def forwards_func(apps, schema_editor):
    from myaapp.models import MyEntity

    db_alias = schema_editor.connection.alias
    entities = MyEntity.objects.using(db_alias).filter(code=None)
    for entity in entities:
        entity.save()


class Migration(migrations.Migration):
     dependencies = [
         ('myapp', '0001_mypreviousmigration'),
     ]

    operations = [
        migrations.RunPython(
            forwards_func, reverse_code=migrations.RunPython.noop
        ),
    ]

References

• Django docs