redmine/rails-2.2/db/migrate/065_add_settings_updated_on.rb

class AddSettingsUpdatedOn < ActiveRecord::Migration
  def self.up
    add_column :settings, :updated_on, :timestamp
    # set updated_on
    Setting.find(:all).each(&:save)
  end

  def self.down
    remove_column :settings, :updated_on
  end
end