Make migration robust to model changes

db/migrate/20130902201853_add_model_to_bike.rb

@@ -3,8 +3,7 @@ class AddModelToBike < ActiveRecord::Migration
     add_column :bikes, :model, :string
     change_column :bikes, :bike_model_id, :integer, :null => true
     Bike.all.each do |bike|
-      bike.model = BikeModel.find_by_id(bike.bike_model_id).model
+      bike.update_attribute(:model, BikeModel.find_by_id(bike['bike_model_id']).model )
-      bike.save
     end
   end
 end