From a11541eb58df7336e54b98b6292b7db50369b0f4 Mon Sep 17 00:00:00 2001
From: Philip Sargent <philip.sargent@klebos.com>
Date: Tue, 5 Jul 2022 14:14:03 +0300
Subject: [PATCH] prefetch_related initial attempts

---
 core/views/scans.py        | 6 ++++++
 templates/manywallets.html | 4 ++++
 2 files changed, 10 insertions(+)

diff --git a/core/views/scans.py b/core/views/scans.py
index 4b35377..097c69f 100644
--- a/core/views/scans.py
+++ b/core/views/scans.py
@@ -58,5 +58,11 @@ def scansingle(request, path, file):
 
 
 def allwallets(request):
+    '''Returns all the wallets in the system, we would like to use
+    the Django queryset SQL optimisation https://docs.djangoproject.com/en/3.2/ref/models/querysets/#prefetch-related
+    to get the related singlescan and survexblock objects but that requires rewriting this to do the query on those, not on
+    the wallets
+    '''
     manywallets = Wallet.objects.all()
+    # manywallets = Wallet.objects.all().prefetch_related('singlescan') fails as the link is defined on 'singlescan' not on 'wallet'
     return render(request, 'manywallets.html', { 'manywallets':manywallets, 'settings': settings })
diff --git a/templates/manywallets.html b/templates/manywallets.html
index 7a61dc4..46dd302 100644
--- a/templates/manywallets.html
+++ b/templates/manywallets.html
@@ -9,6 +9,10 @@
 plans and elevations. It also contains scans of centre-line survex output on which
 hand-drawn passage sections are drawn. These hand-drawn passages will eventually be 
 traced to produce Tunnel or Therion drawings and eventually the final complete cave survey.
+
+<!-- This should all be restructured to use .prefetch_related() and .select_related()
+see https://docs.djangoproject.com/en/3.2/ref/models/querysets/#prefetch-related
+-->
 <table width=95%>
 <tr><th>Scans folder</th><th>Files</th><th>Survex blocks</th><th>Cave</th></tr>
 {% for scanswallet in manywallets %}