# File lib/thinking_sphinx/property.rb, line 64
    def changed?(instance)
      return true if is_string? || @columns.any? { |col| !col.__stack.empty? }
      
      !@columns.all? { |col|
        instance.respond_to?("#{col.__name.to_s}_changed?") &&
        !instance.send("#{col.__name.to_s}_changed?")
      }
    end