Why Does This Nokogiri Xpath Have a Null Return

Why does this Nokogiri XPath have a null return?

The <tbody> tag is an optional tag which is implicit if it is omitted. This means the <tbody> tags are inserted automatically by the browser when not present. They are not in the source code in your example, so nokogiri doesn't know about them.

Firebug uses the generated DOM, which does contains the tbody elements, so the statement does match inside a browser.

Remove both the tbody selectors and you should be fine.

Nokogiri returning nothing when doing an XPath search

The solution to your problem is to get rid of the tbody parts in your xPath, as suggested in "Why does this Nokogiri XPath have a null return?".

Firefox generated tbody elements for you, which is why they appear in Firefox's xPath, but they are not part of the original page source.

Try the following:

response = RestClient.get "http://www.buenosaires.gob.ar/areas/seguridad_justicia/seguridad_urbana/estaciones_servicio/buscador.php?&pag=0"
doc = Nokogiri::HTML(response.body,nil,'utf-8')
doc.remove_namespaces!
table = doc.xpath(".//*[@id='contsinderecha']/form/table/tr[4]/td/table/tr[5]/td/table")

XPath in Nokogiri returning empty array [] whereas I am expecting to have results

Include the namespace information when calling xpath:

doc.xpath("//x:Meta", "x" => "test:com.test.search")

Why does .css work with this Nokogiri object but not XPath?

Assuming case_insensitive_equals does what its name suggests, it is because the class attribute isn’t equal to post-head (case insensitively or not), but it does contain it. XPath treats class attributes as plain strings, it doesn’t split them and handle the classes individually as CSS does.

A simple XPath that would work would be:

doc.xpath('//hgroup[contains(@class, "post-head")]//h2')

(I’ve removed the custom function, you will need to write your own to do this case insensitively.)

This isn’t quite the same though, as it will also match classes such as not-post-head. A more complete XPath would be something like this:

doc.xpath('//hgroup[contains(concat(" ", normalize-space(@class), " "), " post-head ")]//h2')

nokogiri: why is this an invalid xpath?

normalize-space is a function. You can't use it there.

You need a node-set.

maybe you mean

//br/preceding-sibling::*

or you could use normalize-space in a predicate, inside square brackets. Think of the predicate as a filter or selector on the node-set. So you can do this:

//br/preceding-sibling::*[normalize-space()='Fred']

In English that translates to "all elements preceding <br> in the document, and for which the (normalized) text is 'Fred' ". In this document:

<html>
  <p>
    <h2>Fred</h2>
    <br/>
  </p>
  <table>
    <tr>
      <td>
        <br/>
      </td>
    </tr>
  </table>
</html>

...the xpath expression selects the <h2> node.

I figured this out with the free XpathVisualizer tool available on codeplex.

Sample Image

Why does parsing HTML with Nokogiri return a blank?

To answer the question asked, link returns "", because it's an empty NodeSet. In other words, Nokogiri didn't find what you were looking for. A NodeSet behaves like an Array, so when you try to puts an empty array you get "".

Because it's a NodeSet you should iterate over it, as you would an array. (The same is true of your doc.css, which would also return a NodeSet.)

The reason it's empty is because Nokogiri can't find what you want. You're looking for the contents of aa which are:

"audio59779184_153635497_-28469067_16663"

Substituting that into "//input[@id='#{aa}']" gives:

"//input[@id='audio59779184_153635497_-28469067_16663']"

but should be:

"//input[@id='audio_info59779184_153635497_-28469067_16663']"

Searching for that finds content:

 doc.search("//input[@id='audio_info59779184_153635497_-28469067_16663']").size => 1

XPath : Is it possible to return an empty String if elements are not present

In XPath 2.0:

parent/string(definition)

In XPath 1.0 - oh dear, why would anyone want to use XPath 1.0? ;-(

Nokogiri get xpath from Nokogiri::XML::Element

rc is not an element-it's an array of matching elements:

results = rc.map do |node|
  Nokogiri::CSS.xpath_for node.css_path
end

p results

Or, if you know there is only one matching element:

xpath = Nokogiri::CSS.xpath_for rc[0].css_path

Note that xpath_for returns an array, so you will need to extract the first element of the array:

xpath.first

Why Does This Nokogiri Xpath Have a Null Return