--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/gpp/news/utils.py	Sat Mar 26 03:08:05 2011 +0000
@@ -0,0 +1,44 @@
+"""
+Common utility/helper code for the news app.
+
+"""
+from django.contrib.contenttypes.models import ContentType
+
+from comments.models import Comment
+from tagging.models import TaggedItem
+from news.models import Story
+
+
+def attach_extra_attrs(stories):
+    """
+    For each story in the input stories list, attach 2 new attributes:
+    tag_list and comment_count. The tags and comment count info is pulled from
+    the database in bulk. This saves database queries when lots of news
+    stories are displayed at once. For best results, use ".defer('tags')"
+    when retrieve the stories from the database.
+
+    """
+    stories_dict = dict((story.id, story) for story in stories)
+    story_ids = stories_dict.keys()
+
+    # Get all the tags out in one query
+    ct = ContentType.objects.get_for_model(Story)
+    tagged_items = TaggedItem.objects.filter(content_type=ct,
+            object_id__in=story_ids).select_related('tag')
+
+    for story in stories_dict.values():
+        story.tag_list = []
+        story.comment_count = 0
+
+    # attach tags
+    for item in tagged_items:
+        stories_dict[item.object_id].tag_list.append(item.tag.name)
+
+    # Now get all the comment counts out in one fell swoop
+
+    story_ids = Comment.objects.filter(content_type=ct,
+            object_id__in=story_ids).values_list('object_id', flat=True)
+
+    # compute comment_count
+    for story_id in story_ids:
+        stories_dict[story_id].comment_count += 1