still working

models/comment_thread.rb

@@ -29,7 +29,7 @@ class CommentThread
   end
 
   def subscribers
-    subscriptions.map{|s| User.find(s.subscriber_id)}
+    subscriptions.map(&:subscriber)
   end
 
   def to_hash(params={})

models/commentable.rb

@@ -20,7 +20,7 @@ class Commentable
   end
 
   def subscribers
-    subscriptions.map{|s| User.find(s.subscriber_id)}
+    subscriptions.map(&:subscriber)
   end
 
   def to_hash(params={})

models/subscription.rb

@@ -2,9 +2,8 @@ class Subscription
   include Mongoid::Document
   include Mongoid::Timestamps
   
-  field :subscriber_id, type: String
-  field :source_id, type: String
-  field :source_type, type: String
+  belongs_to :subscriber, class_name: "User", autosave: true
+  belongs_to :source, polymorphic: true, autosave: true
 
   index [[:subscriber_id, Mongo::ASCENDING], [:source_id, Mongo::ASCENDING], [:source_type, Mongo::ASCENDING]]
   index [[:source_id, Mongo::ASCENDING], [:source_type, Mongo::ASCENDING]]

models/user.rb

@@ -25,7 +25,7 @@ class User
   end
 
   def followers
-    follower_subscriptions.map{|s| User.find(s.subscriber_id)}
+    follower_subscriptions.map(&:subscriber)
   end
 
   def subscribe(source)