Speed up getting tag's random image

boards/models/image.py

@@ -118,8 +118,6 b' class PostImage(models.Model, Viewable):'
                     str(self.pre_height), str(self.width), str(self.height),
                     full=self.image.url, image_meta=metadata)
 
-    def get_random_associated_post(self, tags=None):
+    def get_random_associated_post(self):
         posts = boards.models.Post.objects.filter(images__in=[self])
-        if tags is not None:
-            posts = posts.filter(threads__tags__in=tags)
         return posts.order_by('?').first()

boards/models/tag.py

@@ -5,7 +5,7 b' from django.core.urlresolvers import rev'
 
 from boards.models.base import Viewable
 from boards.utils import cached_result
-
+import boards
 
 __author__ = 'neko259'
 
@@ -90,3 +90,9 b' class Tag(models.Model, Viewable):'
 
     def get_description(self):
         return self.description
+
+    def get_random_image_post(self):
+        return boards.models.Post.objects.annotate(images_count=Count(
+            'images')).filter(images_count__gt=0, threads__tags__in=[self])\
+                    .order_by('?').first()
+

boards/templates/boards/all_threads.html

@@ -39,10 +39,12 b''
 {% if tag %}
     <div class="tag_info">
         <div class="tag-image">
-            <a href="{{ random_image_post.get_absolute_url }}"><img 
-                src="{{ random_image.image.url_200x150 }}"
-                width="{{ random_image.pre_width }}"
-                height="{{ random_image.pre_height }}"/></a>
+            {% with image=random_image_post.images.first %}
+                <a href="{{ random_image_post.get_absolute_url }}"><img 
+                    src="{{ image.image.url_200x150 }}"
+                    width="{{ image.pre_width }}"
+                    height="{{ image.pre_height }}"/></a>
+            {% endwith %}
         </div>
         <div class="tag-text-data">
             <h2>

boards/views/tag_threads.py

@@ -12,7 +12,6 b" PARAM_HIDDEN_TAGS = 'hidden_tags'"
 PARAM_TAG = 'tag'
 PARAM_IS_FAVORITE = 'is_favorite'
 PARAM_IS_HIDDEN = 'is_hidden'
-PARAM_RANDOM_IMAGE = 'random_image'
 PARAM_RANDOM_IMAGE_POST = 'random_image_post'
 
 __author__ = 'neko259'
@@ -49,9 +48,7 b' class TagView(AllThreadsView, Dispatcher'
         params[PARAM_IS_FAVORITE] = fav_tag_names is not None and tag.name in fav_tag_names
         params[PARAM_IS_HIDDEN] = hidden_tag_names is not None and tag.name in hidden_tag_names
 
-        image = PostImage.objects.get_random_images(1, tags=[tag])[0]
-        params[PARAM_RANDOM_IMAGE] = image
-        params[PARAM_RANDOM_IMAGE_POST] = image.get_random_associated_post(tags=[tag])
+        params[PARAM_RANDOM_IMAGE_POST] = tag.get_random_image_post()
 
         return params