virtual formatted date attribute

formatted_date_attribute.rb

# inspired by http://railsforum.com/viewtopic.php?pid=6676#p6676
module FormattedDateAttribute
  # define virtual formatted date attribute
  # formatted_date_attribute(:start_on, :formatted_start_on, :us_format)
  # formatted_date_attribute(:start_on, :formatted_start_on, "%m/%d/%Y")
  def formatted_date_attribute(attr_name, formatted_name, format)
    define_method(formatted_name) do
      return self[attr_name] unless self[attr_name]
      format.is_a?(Symbol) ? self[attr_name].to_s(format) : self[attr_name].strftime(format)
    end
    define_method("#{formatted_name}=") do |value|
      self[attr_name] = value
    end
  end
end