RubyonRails问题中的序列化表单字段

我的模型中的序列化列在表单中保持正确存在时遇到问题。如果模型验证失败,我希望重新显示“新建”页面,所有模型数据仍在表单中。现在,除了序列化字段之外的所有内容似乎都保持不变(如果我的订单未能购买,则在“新”页上,电子邮件仍被填写,但送货地址字段没有填写)。这是一个Rails bug还是我做错了什么?

我的模型:

class Order < ActiveRecord::Base
    serialize :shipping_address
end

我的控制器:

 def new
   @order = Order.new
 end

def create
  @order = Order.new params[:order]
  if @order.purchase then render :action => "success"
  else render :action => "new"
  end      
end

我的视图,new.html.haml:

= form_for @order do |f|
   - if @order.errors.any?
  #errorExplanation
    %p The following errors occurred:
    %ul
      - for msg in @order.errors.full_messages
        %li= msg
  %h2 Billing Information
  = f.label :email
  = f.text_field :email
  %h2 Shipping Address
  = f.fields_for :shipping_address do |b|
    %p.field.address
      = b.label :address1
      = b.text_field :address1
 %p= f.submit "Place Order"