prefetch_related initial attempts

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 })

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 %}