update_attributes_with_kind.rb

module ActiveRecord
  class KindRollback < Rollback
  end
end

module UpdateAttributesWithKind
  def self.included(model_class)
    model_class.alias_method_chain :update_attributes, :kind
  end
  
  def update_attributes_with_kind(attributes={})
    if attributes.has_key?(:kind)
      switch_kind(attributes[:kind]) do |new_self|
        new_self.update_attributes_without_kind attributes.except(:kind)
        raise ActiveRecord::KindRollback unless new_self.valid?
      end
    else
      update_attributes_without_kind attributes
    end
  end
  
  def switch_kind(kind_name)
    return self if kind_name == self.kind
    old_kind = self.kind
    self.kind = kind_name
    self.save_without_validation
    returning(kind_name.constantize.find(self.id)) { |new_self| yield new_self if block_given? }
  rescue ActiveRecord::KindRollback
    self.kind = old_kind
    self.save_without_validation
    self
  rescue Exception
    self.kind = old_kind
    self.save_without_validation
    raise
  end
end