如何使用Nokogiri访问属性 [英] How to access attributes using Nokogiri

问题描述

我有一个简单的任务来访问某些属性的值。这是一个简单的脚本，它使用 Nokogiri :: XML :: Builder 创建一个简单的XML文档。

I have a simple task of accessing the values of some attributes. This is a simple script that uses Nokogiri::XML::Builder to create a simple XML doc.

require 'nokogiri'

builder = Nokogiri::XML::Builder.new(:encoding => 'UTF-8') do |xml|
  xml.Placement(:messageId => "392847-039820-938777", :system => "MOD", :version => "2.0") {
    xml.objects {
        xml.object(:myattribute => "99", :anotherattrib => "333")
        xml.nextobject_ '9387toot'
        xml.Entertainment "Last Man Standing"
    }
  }
end

puts builder.to_xml
puts builder.root.attributes["messageId"]

结果为：

<?xml version="1.0" encoding="UTF-8"?>
<Placement messageId="392847-039820-938777" version="2.0" system="MOD">
  <objects>
    <object anotherattrib="333" myattribute="99"/>
    <nextobject>9387toot</nextobject>
    <Entertainment>Last Man Standing</Entertainment>
  </objects>
</Placement>
C:/Ruby/lib/ruby/gems/1.8/gems/nokogiri-1.4.2-x86-mingw32/lib/nokogiri/xml/document.rb:178:in `add_child': Document already has a root node (RuntimeError)
    from C:/Ruby/lib/ruby/gems/1.8/gems/nokogiri-1.4.2-x86-mingw32/lib/nokogiri/xml/node.rb:455:in `parent='
    from C:/Ruby/lib/ruby/gems/1.8/gems/nokogiri-1.4.2-x86-mingw32/lib/nokogiri/xml/builder.rb:358:in `insert'
    from C:/Ruby/lib/ruby/gems/1.8/gems/nokogiri-1.4.2-x86-mingw32/lib/nokogiri/xml/builder.rb:350:in `method_missing'
    from C:/Documents and Settings/etrojan/workspace/Lads/tryXPATH2.rb:15

XML是生成的看起来不错。但是，我尝试访问属性会导致生成错误：

The XML that is generated looks fine. However, my attempts to access attributes cause an error to be generated:

Document already has a root node

我不明白为什么 puts 会导致此错误。

I don't understand why puts would cause this error.

推荐答案

使用 Nokogiri :: XML :: Reader 适用于您的示例，但可能不是您要查找的完整答案（请注意，其中有没有生成器的属性方法）。

Using Nokogiri::XML::Reader works for your example, but probably isn't the full answer you are looking for (Note that there is no attributes method for Builder).

reader = Nokogiri::XML::Reader(builder.to_xml)
reader.read #Moves to next node in document
reader.attribute("messageId")

请注意，如果您发出 reader再次读取.read ，然后尝试 reader.attribute（ messageId），结果将为 nil 因为当前节点将不具有此属性。

Note that if you issued reader.read again and then tried reader.attribute("messageId") the result will be nil since the current node will not have this attribute.

您可能想做的是使用 Nokogiri :: XML :: Document （如果要搜索）

What you probably want to do is use Nokogiri::XML::Document if you want to search an XML document by attribute.

doc = Nokogiri::XML(builder.to_xml)
elems = doc.xpath("//*[@messageId]") #get all elements with an attribute of 'messageId'
elems[0].attr('messageId') #gets value of attribute of first elem 

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