Fewer db accesses on transfers list view.

- Add select_related for `from_acc`, `to_acc` and `group.valid_by`.
- 2 requests instead of (3 * #transfers)

kfet/views.py

@@ -1477,19 +1477,32 @@ class SettingsUpdate(SuccessMessageMixin, UpdateView):
         Settings.empty_cache()
         return super(SettingsUpdate, self).form_valid(form)
 
+
 # -----
 # Transfer views
 # -----
 
 @teamkfet_required
 def transfers(request):
-    transfergroups = (TransferGroup.objects
-            .prefetch_related('transfers')
-            .order_by('-at'))
+    transfers_pre = Prefetch(
+        'transfers',
+        queryset=(
+            Transfer.objects
+            .select_related('from_acc', 'to_acc')
+        ),
+    )
+
+    transfergroups = (
+        TransferGroup.objects
+        .select_related('valid_by')
+        .prefetch_related(transfers_pre)
+        .order_by('-at')
+    )
     return render(request, 'kfet/transfers.html', {
         'transfergroups': transfergroups,
     })
 
+
 @teamkfet_required
 def transfers_create(request):
     transfer_formset = TransferFormSet(queryset=Transfer.objects.none())