performance: refactor code shared by episode and emission into a mixin

Cuts down a "Panik sur la ville" episode page from 585 to 23 queries.

panikweb/views.py

@@ -18,18 +18,14 @@ from emissions.models import Category, Emission, Episode, Diffusion, SoundFile,
 from emissions.utils import whatsonair, period_program
 
 
-class EmissionDetailView(DetailView):
-    model = Emission
-
-    def get_context_data(self, **kwargs):
-        context = super(EmissionDetailView, self).get_context_data(**kwargs)
-        context['sectionName'] = "Emissions"
-        context['schedules'] = Schedule.objects.select_related().filter(emission=self.object).order_by('datetime')
+class EmissionMixin:
+    def get_emission_context(self, emission):
+        context = {}
 
         # get all episodes, with an additional attribute to get the date of
         # their first diffusion
         context['episodes'] = \
-                Episode.objects.select_related().filter(emission=self.object
+                Episode.objects.select_related().filter(emission=emission
                     ).extra(select={
                         'first_diffusion': 'emissions_diffusion.datetime',
                         },
@@ -43,7 +39,7 @@ class EmissionDetailView(DetailView):
         # get all related soundfiles in a single query
         soundfiles = {}
         for soundfile in SoundFile.objects.select_related().filter(podcastable=True,
-                fragment=False, episode__emission=self.object):
+                fragment=False, episode__emission=emission):
             soundfiles[soundfile.episode_id] = soundfile
 
         # replace dynamic property by a static attribute, to avoid database
@@ -52,41 +48,30 @@ class EmissionDetailView(DetailView):
             episode.main_sound = soundfiles.get(episode.id)
 
         return context
+
+
+
+class EmissionDetailView(DetailView, EmissionMixin):
+    model = Emission
+
+    def get_context_data(self, **kwargs):
+        context = super(EmissionDetailView, self).get_context_data(**kwargs)
+        context['sectionName'] = "Emissions"
+        context['schedules'] = Schedule.objects.select_related().filter(emission=self.object).order_by('datetime')
+        context.update(self.get_emission_context(self.object))
+        return context
 emission = EmissionDetailView.as_view()
 
-class EpisodeDetailView(DetailView):
+class EpisodeDetailView(DetailView, EmissionMixin):
     model = Episode
 
     def get_context_data(self, **kwargs):
         context = super(EpisodeDetailView, self).get_context_data(**kwargs)
         context['sectionName'] = "Emissions"
-        context['diffusions'] = Diffusion.objects.filter(episode=self.object.id)
-        context['soundfiles'] = SoundFile.objects.filter(episode=self.object.id)
+        context['diffusions'] = Diffusion.objects.select_related().filter(episode=self.object.id)
+        context['soundfiles'] = SoundFile.objects.select_related().filter(episode=self.object.id)
         context['emission'] = Emission.objects.get(slug=self.kwargs.get('emission_slug'))
-        # get all episodes, with an additional attribute to get the date of
-        # their first diffusion
-        context['episodes'] = \
-                Episode.objects.filter(emission=context['emission']
-                    ).extra(select={
-                        'first_diffusion': 'emissions_diffusion.datetime',
-                        },
-                        select_params=(False, True),
-                        where=['''datetime = (SELECT MIN(datetime)
-                                                FROM emissions_diffusion
-                                               WHERE episode_id = emissions_episode.id)'''],
-                        tables=['emissions_diffusion'],
-                    ).order_by('-first_diffusion')
-
-        # get all related soundfiles in a single query
-        soundfiles = {}
-        for soundfile in SoundFile.objects.filter(podcastable=True,
-                fragment=False, episode__emission=Emission.objects.get(slug=self.kwargs.get('emission_slug'))):
-            soundfiles[soundfile.episode_id] = soundfile
-
-        # replace dynamic property by a static attribute, to avoid database
-        # lookups
-        for episode in context['episodes']:
-            episode.main_sound = soundfiles.get(episode.id)
+        context.update(self.get_emission_context(context['emission']))
         return context
 episode = EpisodeDetailView.as_view()