How do I parse XML with Nokogiri css selectors, using loops? - ruby

Question

I am trying to parse this sample XML file:
<Collection version="2.0" id="74j5hc4je3b9">
<Name>A Funfair in Bangkok</Name>
<PermaLink>Funfair in Bangkok</PermaLink>
<PermaLinkIsName>True</PermaLinkIsName>
<Description>A small funfair near On Nut in Bangkok.</Description>
<Date>2009-08-03T00:00:00</Date>
<IsHidden>False</IsHidden>
<Items>
<Item filename="AGC_1998.jpg">
<Title>Funfair in Bangkok</Title>
<Caption>A small funfair near On Nut in Bangkok.</Caption>
<Authors>Anthony Bouch</Authors>
<Copyright>Copyright © Anthony Bouch</Copyright>
<CreatedDate>2009-08-07T19:22:08</CreatedDate>
<Keywords>
<Keyword>Funfair</Keyword>
<Keyword>Bangkok</Keyword>
<Keyword>Thailand</Keyword>
</Keywords>
<ThumbnailSize width="133" height="200" />
<PreviewSize width="532" height="800" />
<OriginalSize width="2279" height="3425" />
</Item>
<Item filename="AGC_1164.jpg" iscover="True">
<Title>Bumper Cars at a Funfair in Bangkok</Title>
<Caption>Bumper cars at a small funfair near On Nut in Bangkok.</Caption>
<Authors>Anthony Bouch</Authors>
<Copyright>Copyright © Anthony Bouch</Copyright>
<CreatedDate>2009-08-03T22:08:24</CreatedDate>
<Keywords>
<Keyword>Bumper Cars</Keyword>
<Keyword>Funfair</Keyword>
<Keyword>Bangkok</Keyword>
<Keyword>Thailand</Keyword>
</Keywords>
<ThumbnailSize width="200" height="133" />
<PreviewSize width="800" height="532" />
<OriginalSize width="3725" height="2479" />
</Item>
</Items>
</Collection>
Here is my current code:
require 'nokogiri'
doc = Nokogiri::XML(File.open("sample.xml"))
somevar = doc.css("collection")
#create loop
somevar.each do |item|
puts "Item "
puts item['Title']
puts "\n"
end#items
Starting at the root of the XML document, I'm trying to go from the root "Collections" down to each new level.
I start in the node sets, and get information from the nodes, and the nodes contain elements. How do I assign the node to a variable, and extract every single layer underneath that and the text?
I can do something like the code below, but I want to know how to systematically move through each nested element of XML using loops, and output the data for each line. When finished showing text, how do I move back up to the previous element/node, whatever it may be (traversing a node in the tree)?
puts somevar.css("Keyworks Keyword").text

Answer 1

Nokogiri's NodeSet and Node support very similar APIs, with the key semantic difference that NodeSet's methods tend to operate on all the contained nodes in turn. For example, while a single node's children gets that node's children, a NodeSet's children gets all contained nodes' children (ordered as they occur in the document). So, to print all the titles and authors of all your items, you could do this:
require 'nokogiri'
doc = Nokogiri::XML(File.open("sample.xml"))
coll = doc.css("Collection")
coll.css("Items").children.each do |item|
title = item.css("Title")[0]
authors = item.css("Authors")[0]
puts title.content if title
puts authors.content if authors
end
You can get at any level of the tree in this way. Another example -- depth-first search printing every node in the tree (NB. the printed representation of a node includes the printed representations of its children, so the output will be quite long):
def rec(node)
puts node
node.children.each do |child|
rec child
end
end
Since you ask about this specifically, if you want to get at the parent of a given node, you can use the parent method. You may never need to though, if you can put your processing in blocks passed to each and the like on NodeSets containing subtrees of interest.