Get a specific tag in a node? - ruby

Question

I'm using Ruby, XPath and Nokogiri and trying to retrieve d1 from the following XML:
<a>
<b1>
<c>
<d1>01/11/2001</d1>
<d2>02/02/2004</d2>
</c>
</b1>
</a>
This is my code in a loop:
rs = doc.xpath("//a/b1/c/d1").inner_text
puts rs
It returns nothing (No error).
I want to get the text in <d1>.

Answer 1

You don't ask for the text content in your xpath query:
rs = doc.xpath('//a/b1/c/d1/text()')

Answer 2

You're misusing XPath:
require 'nokogiri'
doc = Nokogiri::XML(<<EOT)
<a>
<b1>
<c>
<d1>01/11/2001</d1>
<d2>02/02/2004</d2>
</c>
</b1>
</a>
EOT
doc.at('/a/b1/c/d1').text # => "01/11/2001"
doc.at('//d1').text # => "01/11/2001"
// in XPath-ese means start at the top and look anywhere in your document. Instead, if you're supplying an explicit/absolute selector, start at the top of the document and drill down using '/a/b1/c/d1'. Or, do the simple thing and let the parser search through the document for that particular node using //d1. You can do that if you know there's a single instance of that node.
In my code above, I used at instead of xpath. at returns the first matching node, which is similar to using xpath('//d1').first. xpath returns a NodeSet, which is like an array of nodes, whereas at returns a Node only. Using inner_text on a NodeSet is likely to not give you the results you want, which would be the text of a particular node, so be careful there.
doc.xpath('/a/b1/c/d1/text()').class # => Nokogiri::XML::NodeSet
doc.xpath('//c').inner_text # => "\n 01/11/2001\n 02/02/2004\n "
doc.xpath('/a/b1/c/d1').first.text # => "01/11/2001"
Look at the following lines. Instead of using XPath selectors, I used CSS, which tends to be more readable. Nokogiri supports both.
doc.at('d1').text # => "01/11/2001"
doc.at('a b1 c d1').text # => "01/11/2001"
Also, notice the type of data returned from these two lines:
doc.at('/a/b1/c/d1/text()').class # => Nokogiri::XML::Text
doc.at('/a/b1/c/d1').text.class # => String
While it might seem good/smart to tell the parser to locate the text() node inside <d1>, what will be returned isn't text, and will need to be accessed further to make it usable, so consider forgoing the use of text() unless you know exactly why you need it:
doc.at('/a/b1/c/d1/text()').text # => "01/11/2001"
Finally, Nokogiri has many methods used for locating nodes. As I said above, xpath returns a NodeSet and at returns a Node. xpath is really an XPath-specific version of Nokogiri's search method. search, css and xpath all return NodeSets. at, at_css and at_xpath all return Nodes. The CSS and XPath variants are useful when you have an ambiguous selector that you need to be used as CSS or XPath specifically. Most of the time Nokogiri can figure whether it's CSS or XPath on its own and will do the right thing, so it's OK to use the generic search and at for the majority of your coding. Use the specific versions when you have to specify one or the other.