Add subtype to topics to classify private messages

db/migrate/20130416170855_add_subtype_to_topics.rb

@@ -0,0 +1,10 @@
+class AddSubtypeToTopics < ActiveRecord::Migration
+  def up
+    add_column :topics, :subtype, :string
+    execute "update topics set subtype = 'user_to_user' where archetype = 'private_message'"
+  end
+
+  def down
+    remove_column :topics, :subtype
+  end
+end