photo.rb

class Photo < ActiveRecord::Base
    module Statues
      QUEUED = 'queued'
      NEW    = 'new'

      def self.values
        constants.map(&method(:const_get))
      end
      # you can define more special methods as you wanted for Statues
    end

    validates :status, inclusion: {in: Statues.values }

    def change_status
        self.status = Statues::NEW
    end
end