Controller中的NameError

Question

我在尝试运行我编写的代码时遇到错误。它是制作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正常。

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