我如何在表单\u中使用多个“一对多”嵌套属性

考虑到一个用户有很多信用卡,一张信用卡有很多地址,我正在尝试创建一个表单,一次创建一个用户和一张带有地址的信用卡

class User < ActiveRecord::Base
  has_many :credit_cards
  accepts_nested_attributes_for :credit_cards
end

class CreditCard < ActiveRecord::Base
  has_many :addresses
  accepts_nested_attributes_for :addresses
end

控制器代码

def new
  @user = User.new
  @user.credit_cards.build
end

=form_for @user, :url => users_path do |u|
  =u.label :first_name, "Name"
  =u.text_field :first_name
    -u.fields_for :credit_cards do |cc|
      =cc.label :name_on_card, "Name on Card"
      =cc.text_field :name_on_card
      -cc.fields_for :address do |address|
        =address.label :address, "Address"
        =address.text_field :address1

所以我遇到的问题是地址字段没有显示。我试着添加 @user.credit_cards.addresses.build 但我得到一个 undefined method 'build' for nil 错误。