gistfile1.rb

require 'active_support/all'
class AktivRekord
  def self.has_many what
    define_method(what.to_s.pluralize) do
      what.to_s.classify.constantize.find_by_id(self.send("#{what.to_s.singularize}_id"))
    end
  end
end

class Person < AktivRekord
  has_many :books
  def book_id
    5
  end
end

class Book < AktivRekord
  def self.find_by_id(id)
    [Book.new, Book.new]
  end
end


x = Person.new
puts x.books