2015-01-01

Elixir 解析XML的几个坑

在Elixir 1.0.2中解析XML文档的时候,最开始是参考的这个视频, 总之在Google的搜索结果中掉进了无数多个坑后,终于爬出来了.

创建一个项目, 本文所述所有内容都是在文件test/xml_parsing_test.exs文件中完成, 并通过mix test执行测试用例:

root@c87c9967219c:~# mix new xml_parsing
* creating README.md
* creating .gitignore
* creating mix.exs
* creating config
* creating config/config.exs
* creating lib
* creating lib/xml_parsing.ex
* creating test
* creating test/test_helper.exs
* creating test/xml_parsing_test.exs

Your mix project was created successfully.
You can use mix to compile it, test it, and more:

    cd xml_parsing
    mix test

Run `mix help` for more commands.

把我拉出来的是下面这篇Wiki, 视频中的代码有几个问题:

• defrecord关键字废弃了,必须用Record.defrecord

• Record.defrecord不能定义在模块的外面了,必须定义在模块内部, 比如:

  defmodule XmlParsingTest do
      use ExUnit.Case
      require Record
      Record.defrecord :xmlElement, Record.extract(:xmlElement, from_lib: "xmerl/include/xmerl.hrl")
      Record.defrecord :xmlText, Record.extract(:xmlText, from_lib: "xmerl/include/xmerl.hrl")
      ...
  end

• 获取节点值的方式变了

test "Test parsing xml document OLD" do
    {xml, _rest}        = :xmerl_scan.string(:binary.bin_to_list(sample_xml))
    [ title_element ]   = Enum.first(:xmerl_xpath.string('/blog/title', xml)).value
    [ title_text ]      = title_element.content
    title               = title_text.value
    assert title == 'Using xmerl module to parse xml document in elixir'
end
# 对比上下两个测试方法的区别
test "Test parsing xml document NEW" do
    {document, _} = :xmerl_scan.string(String.to_char_list(sample_xml))
    [element] = :xmerl_xpath.string('/blog/title/text()', document)
    assert xmlText(element, :value)  == 'Using xmerl module to parse xml document in elixir'
end

对比上面的代码, 我们通过Record.defrecord定义记录, 该记录是从Erlang的xmerl库中提取的(调用Record.extract), 该记录将作为测试模块的一个函数,我们可以通过下面的方法验证:

运行iex进入Elixir Shell, 并声明模块:

test "Test parsing xml document" do
    # 解析XML文档
    {document, _} = :xmerl_scan.string(String.to_char_list(sample_xml))
    # XPATH查询
    [element] = :xmerl_xpath.string('/blog/title/text()', document)
    # 断言
    assert xmlText(element, :value)  == 'Using xmerl module to parse xml document in elixir'
end

完整的代码

https://gist.github.com/94ce9976fc52e04e572a

完整的项目代码

https://github.com/developerworks/xml_parsing

参考资料

1. ELIXIR AND XML
   http://erlangcentral.org/wiki/index.php?title=Elixir_and_XML
2. 028: Parsing XML
   http://elixirsips.com/episodes/028_parsing_xml.html
3. 常用的XML文档解析模块
   https://github.com/h4cc/awesome-elixir#xml

Elixir

Elixir, XML