fix for bug undefined method 'belongs_to' for Impression:Class

app/models/impression.rb

@@ -1,3 +1,2 @@
 class Impression
-  belongs_to :impressionable, :polymorphic=>true
 end

lib/impressionist/models/active_record/impression.rb

@@ -3,6 +3,8 @@ class Impression < ActiveRecord::Base
   :controller_name, :action_name, :view_name, :request_hash, :ip_address,
   :session_hash, :message, :referrer
 
+  belongs_to :impressionable, :polymorphic=>true
+
   after_save :update_impressions_counter_cache
 
   private

lib/impressionist/models/mongo_mapper/impression.rb

@@ -13,4 +13,6 @@ class Impression
   key :message, String
   key :referrer, String
   timestamps!
+
+  belongs_to :impressionable, :polymorphic=>true
 end