#12795: Introduce a custom Group model (#15304)

* Rename sequences & indexes after renaming users table

* Migrate from auth.Group to a custom group model

* Delete original groups from auth_group table

* Update object & multi-object custom fields referencing the Group model

* Fix ContentType resolution

* Clean up obsolete logic for view/serializer resolution

netbox/users/migrations/0006_custom_group_model.py

@@ -0,0 +1,80 @@
+import users.models
+from django.db import migrations, models
+
+
+def update_custom_fields(apps, schema_editor):
+    """
+    Update any CustomFields referencing the old Group model to use the new model.
+    """
+    ContentType = apps.get_model('contenttypes', 'ContentType')
+    CustomField = apps.get_model('extras', 'CustomField')
+    Group = apps.get_model('users', 'Group')
+
+    if old_ct := ContentType.objects.filter(app_label='users', model='netboxgroup').first():
+        new_ct = ContentType.objects.get_for_model(Group)
+        CustomField.objects.filter(object_type=old_ct).update(object_type=new_ct)
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('users', '0005_alter_user_table'),
+    ]
+
+    operations = [
+        # Create the new Group model & table
+        migrations.CreateModel(
+            name='Group',
+            fields=[
+                ('id', models.BigAutoField(auto_created=True, primary_key=True, serialize=False)),
+                ('name', models.CharField(max_length=150, unique=True)),
+                ('description', models.CharField(blank=True, max_length=200)),
+                ('permissions', models.ManyToManyField(blank=True, related_name='groups', related_query_name='group', to='auth.permission')),
+            ],
+            options={
+                'verbose_name': 'group',
+                'verbose_name_plural': 'groups',
+            },
+            managers=[
+                ('objects', users.models.NetBoxGroupManager()),
+            ],
+        ),
+
+        # Copy existing groups from the old table into the new one
+        migrations.RunSQL(
+            "INSERT INTO users_group (SELECT id, name, '' AS description FROM auth_group)"
+        ),
+
+        # Update the sequence for group ID values
+        migrations.RunSQL(
+            "SELECT setval('users_group_id_seq', (SELECT MAX(id) FROM users_group))"
+        ),
+
+        # Update the "groups" M2M fields on User & ObjectPermission
+        migrations.AlterField(
+            model_name='user',
+            name='groups',
+            field=models.ManyToManyField(blank=True, related_name='users', related_query_name='user', to='users.group'),
+        ),
+        migrations.AlterField(
+            model_name='objectpermission',
+            name='groups',
+            field=models.ManyToManyField(blank=True, related_name='object_permissions', to='users.group'),
+        ),
+
+        # Delete groups from the old table
+        migrations.RunSQL(
+            "DELETE from auth_group"
+        ),
+
+        # Update custom fields
+        migrations.RunPython(
+            code=update_custom_fields,
+            reverse_code=migrations.RunPython.noop
+        ),
+
+        # Delete the proxy model
+        migrations.DeleteModel(
+            name='NetBoxGroup',
+        ),
+    ]