enforce a stable list order when attaching/detaching instance groups

awx/main/migrations/0074_v360_migrate_instance_group_relations.py

@@ -0,0 +1,42 @@
+# -*- coding: utf-8 -*-
+# Generated by Django 1.11.20 on 2019-05-06 13:49
+from __future__ import unicode_literals
+
+from django.db import migrations
+
+
+def create_through_relations(apps, schema_editor):
+    relations = [
+        [
+            'UnifiedJobTemplate',
+            apps.get_model('main', 'UnifiedJobTemplateInstanceGroupMembership'),
+        ],
+        [
+            'Organization',
+            apps.get_model('main', 'OrganizationInstanceGroupMembership'),
+        ],
+        [
+            'Inventory',
+            apps.get_model('main', 'InventoryInstanceGroupMembership'),
+        ],
+    ]
+    for cls, Membership in relations:
+        Target = apps.get_model('main', cls)
+        for x in Target.objects.iterator():
+            for i, instance_group in enumerate(x.instance_groups.all()):
+                Membership(
+                    instancegroup=instance_group,
+                    position=i,
+                    **{'%s' % cls.lower(): x}
+                ).save()
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('main', '0073_v360_create_instance_group_m2m'),
+    ]
+
+    operations = [
+        migrations.RunPython(create_through_relations)
+    ]