棄用警告創建屬性「貨幣」

我使用的錢護欄寶石的Rails 3.2.3，我已經得到了它具有以下產品型號：棄用警告創建屬性「貨幣」

我的模型

class Product < ActiveRecord::Base 
    attr_accessible :name, :price 

    composed_of :price, 
    :class_name => "Money", 
    :mapping => [%w(price_cents cents), %w(currency currency_as_string)], 
    :constructor => Proc.new { |cents, currency| Money.new(cents || 0, currency || Money.default_currency) }, 
    :converter => Proc.new { |value| value.respond_to?(:to_money) ? value.to_money : raise(ArgumentError, "Can't convert #{value.class} to Money") } 


end

我的測試

require 'spec_helper' 

describe Product do 
    context "testing money gem" do 
    it "creates product with price" do 
     product = Product.create(:price => 200) 
     product.price.should eq(200) 
     product.price_cents.should eq(20000) 
    end 
    end 
end

棄用警告我收到了。

% rspec spec/models/product_spec.rb 

Product 
    testing money gem 
DEPRECATION WARNING: You're trying to create an attribute `currency'. Writing arbitrary attributes on a model is deprecated. Please just use `attr_writer` etc. (called from block (3 levels) in <top (required)> at /home/map7/project/spec/models/product_spec.rb:6) 
    creates product with price 

Finished in 0.06682 seconds 
1 example, 0 failures

如何解決此棄用警告？

更新

如果我添加「貨幣」，以它開始工作表。我應該這樣做嗎？

來源

2012-05-15 map7