Don't pull and sort mirror URLs unless we have to

On the download page, the explicit sorted() call was forcing evaluation
of the Django queryset, even if we never actually needed the results
because the template fragment was cached. Wrap it all in a callable
function which looks the same to the template, but saves us the cost of
evaluation every single page view.

Signed-off-by: Dan McGee <dan@archlinux.org>

1 files changed, 10 insertions, 5 deletions

diff --git a/public/views.py b/public/views.py
index e15f5b89..3c823c9d 100644
--- a/public/views.py
+++ b/public/views.py
@@ -82,11 +82,16 @@ def download(request):
         release = Release.objects.filter(available=True).latest()
     except Release.DoesNotExist:
         release = None
-    mirror_urls = MirrorUrl.objects.select_related('mirror').filter(
-            protocol__default=True,
-            mirror__public=True, mirror__active=True, mirror__isos=True)
-    sort_by = attrgetter('country.name', 'mirror.name')
-    mirror_urls = sorted(mirror_urls, key=sort_by)
+
+    def mirror_urls():
+        '''In order to ensure this is lazily evaluated since we can't do
+        sorting at the database level, make it a callable.'''
+        urls = MirrorUrl.objects.select_related('mirror').filter(
+                protocol__default=True,
+                mirror__public=True, mirror__active=True, mirror__isos=True)
+        sort_by = attrgetter('country.name', 'mirror.name')
+        return sorted(urls, key=sort_by)
+
     context = {
         'release': release,
         'releng_iso_url': settings.ISO_LIST_URL,