A snibbet of docunext/svxbox/lib/svxbox/roary.rb as an example of ActiveSupport::Concern.

roary-snibbet.rb

module SvxBox::Roary
  extend ActiveSupport::Concern

  included do
    cattr_accessor :param_suffix
    before_validation :ensure_param_key_has_value, :if => :param_key_attribute?
    validates :param_key, :presence => true, :uniqueness => true, :if => :param_key_attribute?
  end

  # ...


  #   class Something < ActiveRecord::Base
  #     include SvxBox::Roary
  #     to_param_suffix :name
  #
  #   end
  module ClassMethods

    # ...

    def find(key)
      return super if !self.attribute_method?(:param_key)
      begin
        where("param_key = ?", key.to_s).first!
      rescue ActiveRecord::RecordNotFound
        super
      end
    end
  end
end