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"]
The results are:
<?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
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
I don't understand why puts
would cause this error.
Nokogiri makes an attempt to determine whether a CSS or XPath selector is being passed in. It's possible to create a selector that fools at or search so occasionally it will misunderstand, which is why we have the more specific versions of the methods.
One of the best gems for Ruby on Rails is Nokogiri which is a library to deal with XML and HTML documents. The most common use for a parser like Nokogiri is to extract data from structured documents.
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")
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.
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
Here is a slightly more succinct way to access attributes using Nokogiri
(assuming you already have your xml stored in a variable called xml
, as covered by @atomicules' answer):
xml.xpath("//Placement").attr("messageId")
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