cache addon.get_category for firefox (bug 650972)

apps/addons/models.py

@@ -251,6 +251,7 @@ def __init__(self, *args, **kw):
         # Make sure all add-ons have a slug.  save() runs clean_slug.
         if self.id and not self.slug:
             self.save()
+        self._first_category = {}
 
     def save(self, **kw):
         self.clean_slug()
@@ -387,6 +388,8 @@ def reviews(self):
         return Review.objects.filter(addon=self, reply_to=None)
 
     def get_category(self, app):
+        if app in self._first_category:
+            return self._first_category[app]
         categories = list(self.categories.filter(application=app))
         return categories[0] if categories else None
 
@@ -590,6 +593,16 @@ def transformer(addons):
         for addon, previews in itertools.groupby(qs, lambda x: x.addon_id):
             addon_dict[addon].all_previews = list(previews)
 
+        # Attach _first_category for Firefox.
+        for addon in addons:
+            addon._first_category[amo.FIREFOX.id] = None
+        qs = AddonCategory.objects.filter(
+            addon__in=addon_dict, category__application=amo.FIREFOX.id)
+        for cat in qs.select_related('category'):
+            addon = addon_dict[cat.addon_id]
+            addon._first_category[amo.FIREFOX.id] = cat.category
+
+
     @property
     def show_beta(self):
         return self.status == amo.STATUS_PUBLIC and self.current_beta_version

apps/addons/templates/addons/impala/addon_grid.html

@@ -16,7 +16,11 @@
           </div>
           <div class="summary">
             <h3>{{ addon.name }}</h3>
-            <div class="category" class="more-info">{{ addon.get_category(APP.id) }}</div>
+            {% with cat = addon.get_category(APP.id) %}
+              {% if cat %}
+                <div class="category" class="more-info">{{ cat }}</div>
+              {% endif %}
+            {% endwith %}
             <div class="rating">{{ addon.average_rating|stars }} ({{ addon.total_reviews|numberfmt }})</div>
           </div>
         </a>