gistfile1.rb

module OrderedModel
  def up
    self.class.update_all 'ord = ord + 1', "ord = #{self.ord-1}"
    update_attribute :ord, self.ord-1
  end

  def down
    self.class.update_all 'ord = ord - 1', "ord = #{self.ord+1}"
    update_attribute :ord, self.ord+1
  end

  def set_ord
    self.class.update_all 'ord = ord - 1', "ord > #{self.ord}"
  end

end

class Gallery < ActiveRecord::Base
  include OrderedModel
  has_many :photos
  before_destroy :set_ord
end