Question

Here’s the XML I’m working with:

<order xmlns="http://example.com/schemas/1.0">
  <link type="application/xml" rel="http://example.com/rel/self" href="https://example.com/orders/1631"/>
  <link type="application/xml" rel="http://example.com/rel/order/history" href="http://example.com/orders/1631/history"/>
  <link type="application/xml" rel="http://example.com/rel/order/transition/release" href="https://example.com/orders/1631/release"/>
  <link type="application/xml" rel="http://example.com/rel/order/transition/cancel" href="https://example.com/orders/1631/cancel"/>
  <state>hold</state>
  <order-number>123-456-789</order-number>
  <survey-title>Testing</survey-title>
  <survey-url>http://example.com/s/123456</survey-url>
  <number-of-questions>6</number-of-questions>
  <number-of-completes>100</number-of-completes>
  <target-group>
    <country>
      <id>US</id>
      <name>United States</name>
    </country>
    <min-age>15</min-age>
  </target-group>
  <quote>319.00</quote>
  <currency>USD</currency>
</order>

What I need to do is get the href attribute, from the link that has a rel of http://example.com/rel/order/transition/release

So, how can I do that using Nokogiri?

Answer 1

Easy-peasy:

require 'nokogiri'

doc = Nokogiri::XML(<<EOT)
<order xmlns="http://example.com/schemas/1.0">
  <link type="application/xml" rel="http://example.com/rel/self" href="https://example.com/orders/1631"/>
  <link type="application/xml" rel="http://example.com/rel/order/history" href="http://example.com/orders/1631/history"/>
  <link type="application/xml" rel="http://example.com/rel/order/transition/release" href="https://example.com/orders/1631/release"/>
  <link type="application/xml" rel="http://example.com/rel/order/transition/cancel" href="https://example.com/orders/1631/cancel"/>
  <state>hold</state>
  <order-number>123-456-789</order-number>
  <survey-title>Testing</survey-title>
  <survey-url>http://example.com/s/123456</survey-url>
  <number-of-questions>6</number-of-questions>
  <number-of-completes>100</number-of-completes>
  <target-group>
    <country>
      <id>US</id>
      <name>United States</name>
    </country>
    <min-age>15</min-age>
  </target-group>
  <quote>319.00</quote>
  <currency>USD</currency>
</order>
EOT

href = doc.at('link[rel="http://example.com/rel/order/transition/release"]')['href']
=> "https://example.com/orders/1631/release"

This is using Nokogiri’s ability to use CSS accessors. Sometimes it’s easier (or the only way) to use XPath, but I prefer CSS because they tend to be more readable.

Nokogiri::Node.at can take a CSS accessor or XPath, and will return the first node matching that pattern. If you need to iterate over all the matches, use search instead, which returns a NodeSet, which you can treat as an array. Nokogiri also supports at_xpath and at_css along with css and xpath for at and search symmetry.