Add a position number to the OrderPosition model

src/pretix/base/migrations/0050_orderposition_positionid.py

@@ -0,0 +1,31 @@
+# -*- coding: utf-8 -*-
+# Generated by Django 1.10.4 on 2016-12-21 17:05
+from __future__ import unicode_literals
+
+from django.db import migrations, models
+
+
+def forwards(apps, schema_editor):
+    Order = apps.get_model('pretixbase', 'Order')
+    for o in Order.objects.all():
+        for i, p in enumerate(o.positions.all()):
+            p.positionid = i + 1
+            p.save()
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('pretixbase', '0049_checkin'),
+    ]
+
+    operations = [
+        migrations.AddField(
+            model_name='orderposition',
+            name='positionid',
+            field=models.PositiveIntegerField(default=1),
+        ),
+        migrations.RunPython(
+            forwards, migrations.RunPython.noop
+        ),
+    ]