steps.rb

class Orders::Step1Controller < PublicController
  def new
    
  end
  
  def create
    
  end
  
protected
  
  def order
    @order ||= Order::Step1.new(Order.new(params[:order]))
  end
end

class Orders::Step2Controller < PublicController
  def new
    
  end
  
  def create
    
  end
  
protected
  
  def order
    @order ||= Order::Step2.new(Order.find(session[:order_id]))
  end
end

class Order::Step1 < SimpleDelegator
  validates :first_name, :presence => true
end

class Order::Step2 < SimpleDelegator
  validates :card_number, :with => CreditCardValidator
end