Optimise SQL requests in counter.get view

counter/templates/counterTemplate.html

                 </a>
                 {% if not counter.lastReset.noSeum %}
                 {% if counter.alreadyLiked %}
-                <span class="pull-right badge" {% if counter.likeCount > 0 %} data-toggle="tooltip" data-placement="top" title="{{ counter.likersString }}" {% endif %}>
-                    <span class="glyphicon glyphicon-ok"></span>&emsp;{{ counter.likeCount }}
+                <span class="pull-right badge" {% if counter.likes_count > 0 %} data-toggle="tooltip" data-placement="top" title="{{ counter.likersString }}" {% endif %}>
+                    <span class="glyphicon glyphicon-ok"></span>&emsp;{{ counter.likes_count }}
                 </span>
                 {% elif counter.id == myCounter.id or counter.lastReset.who.id == myCounter.id %}
-                <span class="pull-right badge" {% if counter.likeCount > 0 %} data-toggle="tooltip" data-placement="top" title="{{ counter.likersString }}" {% endif %}>
-                    <span class="glyphicon glyphicon-heart"></span>&emsp;{{ counter.likeCount }}
+                <span class="pull-right badge" {% if counter.likes_count > 0 %} data-toggle="tooltip" data-placement="top" title="{{ counter.likersString }}" {% endif %}>
+                    <span class="glyphicon glyphicon-heart"></span>&emsp;{{ counter.likes_count }}
                 </span>
                 {% else %}
                 <a class="pull-right badge" onclick="document.forms['like{{counter.id}}'].submit();">
-                    <span class="glyphicon glyphicon-heart"></span>&emsp;{{ counter.likeCount }}
+                    <span class="glyphicon glyphicon-heart"></span>&emsp;{{ counter.likes_count }}
                 </a>
                 {% endif %}
                 {% endif %}
                       {{ reset.who.trigramme }}
                     {% endif %}
                   </td>
-                  <td>{{ reset.likeCount }}</td>
+                  <td>{{ reset.likes_count }}</td>
                 </tr>
               {% endfor %}
             </tbody>

counter/views/counter.py

 from datetime import datetime, timedelta
-import copy
+from copy import copy
 
 from django.contrib.auth.decorators import login_required
 from django.core.mail import EmailMessage
 from django.core.urlresolvers import reverse
+from django.db.models import Count, Prefetch
 from django.http import HttpResponseRedirect
 from django.shortcuts import render
 from django.template.loader import render_to_string
     except Counter.DoesNotExist:
         return HttpResponseRedirect(reverse('login'))
 
-    counter = Counter.objects.prefetch_related('resets', 'resets__likes').get(pk=id_counter)
-    resets = counter.resets.order_by('-timestamp')
-    timezero = timedelta(0)
+    counter = Counter.objects.prefetch_related(
+        # we get the related resets annotated with their number of likes
+        Prefetch('resets', queryset=Reset.objects.annotate(likes_count=Count('likes'))),
+        'resets__likes'
+    ).get(pk=id_counter)
+    resets = list(counter.resets.order_by('-timestamp'))
 
     # Display
-    if resets.count() == 0:
+    if len(resets) == 0:
         counter.lastReset = Reset()
-        counter.lastReset.delta = timezero
+        counter.lastReset.delta = timedelta(0)
         counter.lastReset.noSeum = True
         seumFrequency = _('unknown')
     else:
-        firstReset = resets.reverse()[0]
+        firstReset = copy(resets[-1])
         counter.lastReset = resets[0]
         counter.lastReset.noSeum = False
         if counter.lastReset.who is None or counter.lastReset.who == counter:
             counter.lastReset.selfSeum = False
 
         counter.lastReset.formatted_delta = arrow.Arrow.fromdatetime(counter.lastReset.timestamp).humanize(locale=get_language())
-        counter.seumCount = counter.resets.count()
+        counter.seumCount = len(resets)
         seumFrequency = format_timedelta((datetime.now() - firstReset.timestamp.replace(tzinfo=None)) / counter.seumCount,
             locale=get_language(), threshold=1)
 
             counter.likersString = ", ".join(like.liker.trigramme for like in counter.lastLikes)
 
     for reset in resets:
-        if reset.who is None or reset.who == reset.counter:
+        if reset.who is None or reset.who.id == reset.counter.id:
             reset.selfSeum = True
         else:
             reset.selfSeum = False
         reset.date = reset.timestamp
-        reset.likeCount = reset.likes.count()
 
     # Timeline graph
     # Data pre-processing