Controller中的NameError

我在尝试运行我编写的代码时遇到错误。 它是生成xml文件的代码，它从数据库中读取以获取所有信息。 错误是由两行，Document.new和Element.new引起的

如果我注释掉这两行，那么代码就可以了。 我不确定为什么这样做，因为那些类应该工作得很好。

我的代码如下：

def create_google_file @products = Product.find(:all) file = File.new('dir.xml','w') doc = Document.new root = Element.new "rss" root.add_attribute("xmlns:g", "http://base.google.com/ns/1.0") root.add_attribute("version", "2.0") channel = Element.new "channel" root.add_element channel title = Element.new "title" title.text = "Sample Google Base" channel.add_element title link = Element.new "link" link.text = "http://base.google.com/base/" channel.add_element link description = Element.new "description" description.text = "Information about products" channel.add_element description @products.each do |y| item = channel.add_element("item") id = item.add_element("g:id") id.text = y.id title = item.add_element("title") title.text = y.title description = item.add_element("description") description.text = y.description googlecategory = item.add_element("g:google_product_category") googlecategory.text = y.googlecategory producttype = item.add_element("g:product_type") producttype.text = y.producttype link = item.add_element("link") link.text = y.link imglink = item.add_element("g:image_link") imglink.text = y.imglink condition = item.add_element("condition") condition.text = y.condition availability = item.add_element("g:availability") availability.text = y.availability price = item.add_element("g:price") price.text = y.price "USD" gtin = item.add_element("g:gtin") gtin.text = y.gtin brand = item.add_element("g:brand") brand.text = y.brand mpn = item.add_element("g:mpn") mpn.text = y.mpn expirationdate = item.add_element("g:expiration_date") expirationdate.text = y.salepricedate end doc.add_element root file.puts doc file.close end 

我得到的错误是：ProductsController＃create_google_file中的NameError

未初始化的常量ProductsController :: Element

和

ProductsController＃create_google_file中的NameError

未初始化的常量ProductsController :: Document