Example of Act As Recomendable

gistfile1.rb

 class Book < ActiveRecord::Base
    has_many :user_books
    has_many :users, :through => :user_books
  end

  class UserBook < ActiveRecord::Base
    belongs_to :book
    belongs_to :user
  end

  class User < ActiveRecord::Base
    has_many :user_books
    has_many :books, :through => :user_books
    acts_as_recommendable :books, :through => :user_books
  end

  user = User.find(:first)
  user.similar_users #=> [...]
  user.recommended_books #=> [...]