Remove Event.purchase_order in favour of a simple EventAuthorisation object.

RIGS/migrations/0028_migrate_purchase_order.py

@@ -0,0 +1,47 @@
+# -*- coding: utf-8 -*-
+from __future__ import unicode_literals
+
+from django.db import models, migrations
+from django.db.models import F, Sum, DecimalField
+
+
+def POs_forward(apps, schema_editor):
+    VatRate = apps.get_model('RIGS', 'VatRate')
+    Event = apps.get_model('RIGS', 'Event')
+    EventItem = apps.get_model('RIGS', 'EventItem')
+    EventAuthorisation = apps.get_model('RIGS', 'EventAuthorisation')
+    db_alias = schema_editor.connection.alias
+    for event in Event.objects.using(db_alias).filter(purchase_order__isnull=False):
+        sum_total = EventItem.objects.filter(event=event).aggregate(
+            sum_total=Sum(models.F('cost') * F('quantity'),
+                          output_field=DecimalField(
+                              max_digits=10,
+                              decimal_places=2)
+                          )
+        )['sum_total']
+
+        vat = VatRate.objects.using(db_alias).filter(start_at__lte=event.start_date).latest()
+        total = sum_total + sum_total * vat.rate
+
+        EventAuthorisation.objects.using(db_alias).create(event=event, name='LEGACY',
+                                                          email='treasurer@nottinghamtec.co.uk',
+                                                          amount=total)
+
+
+def POs_reverse(apps, schema_editor):
+    EventAuthorisation = apps.get_model('RIGS', 'EventAuthorisation')
+    db_alias = schema_editor.connection.alias
+    for auth in EventAuthorisation.objects.using(db_alias).filter(po__isnull=False):
+        auth.event.purchase_order = auth.po
+        auth.delete()
+
+
+class Migration(migrations.Migration):
+    dependencies = [
+        ('RIGS', '0027_eventauthorisation_event_singular'),
+    ]
+
+    operations = [
+        migrations.RunPython(POs_forward, POs_reverse),
+        migrations.RemoveField(model_name='event', name='purchase_order')
+    ]