rework main_sound prefetching

panikweb/views.py

@@ -49,14 +49,18 @@ class EmissionMixin:
 
         # get all related soundfiles in a single query
         soundfiles = {}
+        if episode_ids is not None:
+            for episode_id in episode_ids:
+                soundfiles[episode_id] = None
+        else:
+            for episode in Episode.objects.filter(emission=emission):
+                soundfiles[episode.id] = None
+
         for soundfile in SoundFile.objects.select_related().filter(podcastable=True,
                 fragment=False, episode__emission=emission):
             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)
+        Episode.set_prefetched_soundfiles(soundfiles)
 
         #context['futurEpisodes'] = context['episodes'].filter(first_diffusion='2013')[0:3]