Code to create an ActiveRecord object by calling create on a base class but actually getting a child class object based on the type attribute provided.

gistfile1.rb

class Element < ActiveRecord::Base

  # This code lets us create the right type of class by passing in :type
  # eg:  Element.new(:type => 'TitleElement') will crteate a TitleElement
  class << self
    def class_from_args(a)
      if (h = a.first).is_a? Hash and (type = h[:type] || h['type']) and (klass = type.constantize) != self
        raise "Unknown type" unless klass < self # klass should be a descendant of us
        return klass
      end
    end

    def new_with_cast(*a, &b)
      klass = class_from_args(a)
      klass ? klass.new(*a, &b) : new_without_cast(*a, &b)
    end
    alias_method_chain :new, :cast

    def create_with_cast(*a, &b)
      klass = class_from_args(a)
      klass ? klass.create(*a, &b) : create_without_cast(*a, &b)
    end
    alias_method_chain :create, :cast
  end

end