netbox/netbox/ipam/migrations/0071_prefix_scope.py

import django.db.models.deletion
from django.db import migrations, models


def copy_site_assignments(apps, schema_editor):
    """
    Copy site ForeignKey values to the scope GFK.
    """
    ContentType = apps.get_model('contenttypes', 'ContentType')
    Prefix = apps.get_model('ipam', 'Prefix')
    Site = apps.get_model('dcim', 'Site')
    db_alias = schema_editor.connection.alias

    Prefix.objects.using(db_alias).filter(site__isnull=False).update(
        scope_type=ContentType.objects.get_for_model(Site),
        scope_id=models.F('site_id')
    )


class Migration(migrations.Migration):
    dependencies = [
        ('contenttypes', '0002_remove_content_type_name'),
        ('ipam', '0070_vlangroup_vlan_id_ranges'),
    ]

    operations = [
        # Add the `scope` GenericForeignKey
        migrations.AddField(
            model_name='prefix',
            name='scope_id',
            field=models.PositiveBigIntegerField(blank=True, null=True),
        ),
        migrations.AddField(
            model_name='prefix',
            name='scope_type',
            field=models.ForeignKey(
                blank=True,
                null=True,
                on_delete=django.db.models.deletion.PROTECT,
                related_name='+',
                to='contenttypes.contenttype',
            ),
        ),
        # Copy over existing site assignments
        migrations.RunPython(code=copy_site_assignments, reverse_code=migrations.RunPython.noop),
    ]