Dynamic scopes injection

gistfile1.rb

module BookScopes

  def self.extended(base)
    base.instance_exec &scope_definitions
  end

  def self.included(base)
    base.class_exec &scope_definitions
  end

  def self.scope_definitions
    lambda do

      class << self

        def most_recent
          order("created_at DESC").limit(1)
        end

      end
      
    end
  end

end

class Book < ActiveRecord::Base

  include BookScopes

  belongs_to :library
  
end

Book.most_recent

# or

class Library < ActiveRecord::Base

  has_many :books

  def self.find_most_recent_books
    books.scoped.extend(BookScopes).most_recent
  end

end

Library.first.find_most_recent_books