Fallback when original is not present or somethings not right.
For normal Object's and ActiveRecord's.

class User < ActiveRecord::Base
  include Fallback

  # use description if detailed description is not available
  fallback :detailed_description => :description

  has_one :shop

  # use shop.name if user.name is blank
  fallback :name, :to => :shop

  # use shop.title if user.name is blank
  fallback :name => :title, :to => :shop

  # use shop.title if lambda is true (also works with :unless)
  fallback :title, :to => :shop, :if => lambda{|user| user.title.size < 10 }

  # use shop.title if user.title_to_short? is true
  fallback :title, :to => :shop, :if => :title_to_short?
end

Install

Gem sudo gem install fallback
Or as Rails plugin: script/plugin install git://github.com/grosser/fallback.git

Author

Michael Grosser
grosser.michael@gmail.com
Hereby placed under public domain, do what you want, just do not hold me accountable...