don't use .last(3), use .limit(3) instead. also, don't put an order on an...

don't use .last(3), use .limit(3) instead.  also, don't put an order on an association as it isn't overridable.  (this commit minimizes AR object instantiation in the stream)

app/models/post.rb

@@ -67,7 +67,9 @@ class Post < ActiveRecord::Base
   # gives the last three comments on the post
   def last_three_comments
     return if self.comments_count == 0
-    self.comments.includes(:author => :profile).last(3)
+    # DO NOT USE .last(3) HERE.  IT WILL FETCH ALL COMMENTS AND RETURN THE LAST THREE
+    # INSTEAD OF DOING THE FOLLOWING, AS EXPECTED (THX AR):
+    self.comments.order('created_at DESC').limit(3).includes(:author => :profile).reverse!
   end
 
   def self.excluding_blocks(user)

lib/diaspora/commentable.rb

@@ -6,7 +6,7 @@ module Diaspora
   module Commentable
     def self.included(model)
       model.instance_eval do
-        has_many :comments, :as => :commentable, :order => 'created_at', :dependent => :destroy
+        has_many :comments, :as => :commentable, :dependent => :destroy
       end
     end