Refactor outstanding invoice query to use django annotations.

Considerably improves performance and also removes the explict PSQL code.

Can be further improved by reducing the number of hits to the db in the template.

RIGS/finance.py

@@ -4,13 +4,13 @@ import re
 
 from django.contrib import messages
 from django.core.urlresolvers import reverse_lazy
+from django.db.models import Count, Sum, F, FloatField, Q, Value
 from django.http import Http404, HttpResponseRedirect
 from django.http import HttpResponse
 from django.shortcuts import get_object_or_404
 from django.template import RequestContext
 from django.template.loader import get_template
 from django.views import generic
-from django.db.models import Q
 from z3c.rml import rml2pdf
 
 from RIGS import models
@@ -30,18 +30,13 @@ class InvoiceIndex(generic.ListView):
         return context
 
     def get_queryset(self):
-        # Manual query is the only way I have found to do this efficiently. Not ideal but needs must
+        query = self.model.objects.annotate(
-        sql = "SELECT * FROM " \
+            cost=Sum(F('event__items__cost') * F('event__items__quantity'), output_field=FloatField()),
-              "(SELECT " \
+            payment_count=Count('payment'),
-              "(SELECT COUNT(p.amount) FROM \"RIGS_payment\" AS p WHERE p.invoice_id=\"RIGS_invoice\".id) AS \"payment_count\", " \
+            payments=Sum('payment__amount'),
-              "(SELECT SUM(ei.cost * ei.quantity) FROM \"RIGS_eventitem\" AS ei WHERE ei.event_id=\"RIGS_invoice\".event_id) AS \"cost\", " \
+        ).filter(
-              "(SELECT SUM(p.amount) FROM \"RIGS_payment\" AS p WHERE p.invoice_id=\"RIGS_invoice\".id) AS \"payments\", " \
+            Q(cost__gt=0.0, payment_count=0) | Q(cost__lt=Value('payments'), cost__gt=Value('payments'))
-              "\"RIGS_invoice\".\"id\", \"RIGS_invoice\".\"event_id\", \"RIGS_invoice\".\"invoice_date\", \"RIGS_invoice\".\"void\" FROM \"RIGS_invoice\") " \
+        ).select_related('event', 'event__organisation', 'event__person', 'event__venue')
-              "AS sub " \
-              "WHERE (((cost > 0.0) AND (payment_count=0)) OR (cost - payments) <> 0.0) AND void = '0'" \
-              "ORDER BY invoice_date"
-
-        query = self.model.objects.raw(sql)
 
         return query
 
@@ -94,6 +89,7 @@ class InvoiceVoid(generic.View):
             return HttpResponseRedirect(reverse_lazy('invoice_list'))
         return HttpResponseRedirect(reverse_lazy('invoice_detail', kwargs={'pk': object.pk}))
 
+
 class InvoiceDelete(generic.DeleteView):
     model = models.Invoice
 
@@ -114,6 +110,7 @@ class InvoiceDelete(generic.DeleteView):
     def get_success_url(self):
         return self.request.POST.get('next')
 
+
 class InvoiceArchive(generic.ListView):
     model = models.Invoice
     template_name = 'RIGS/invoice_list_archive.html'
@@ -142,11 +139,11 @@ class InvoiceWaiting(generic.ListView):
         events = self.model.objects.filter(
             (
                 Q(start_date__lte=datetime.date.today(), end_date__isnull=True) |  # Starts before with no end
-                Q(end_date__lte=datetime.date.today()) # Has end date, finishes before
+                Q(end_date__lte=datetime.date.today())  # Has end date, finishes before
-            ) & Q(invoice__isnull=True) # Has not already been invoiced
+            ) & Q(invoice__isnull=True)  # Has not already been invoiced
-            & Q(is_rig=True) # Is a rig (not non-rig)
+            & Q(is_rig=True)  # Is a rig (not non-rig)
-            
+
-            ).order_by('start_date') \
+        ).order_by('start_date') \
             .select_related('person',
                             'organisation',
                             'venue', 'mic') \