how to use xpath? (nokogiri)

Question

I have not found any documentation nor tutorial for that. Does anything like that exist?

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doc.xpath('//table/tbody[@id="threadbits_forum_251"]/tr')

the code above will get me any table, anywhere, that has a tbody child with the attribute id equal to threadbits_forum_251. But why does it start with double //? why there is /tr at the end? See for more details

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Could anybody tell me how to extract href, id, alt, src etc using nokogiri?

td[3]/div[1]/a/text()' <--- extracts text

but how can I extract other things?

Answer 1

Seems you need to read a XPath Tutorial

Your //table/tbody[@id="threadbits_forum_251"]/tr expression means:

• // - Anywhere in your XML document
• table/tbody - take a table element with a tbody child
• [@id="threadbits_forum_251"] - where id attribute are equals to "threadbits_forum_251"
• tr - and take its tr elements

So, basically, you need to know:

• attributes begins with @
• conditions go inside [] brackets

If I correcly understood that API, you can go with doc.xpath("td[3]/div[1]/a")["href"], or td[3]/div[1]/a/@href if there is just one <a> element.

Answer 2

your xpath is correct and you seem to have answered your own question's first part (almost):

doc.xpath('//table/tbody[@id="threadbits_forum_251"]/tr')

"the code above will get me any table table's tr, anywhere, that has a tbody child with the attribute id equal to threadbits_forum_251"

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// means the following element can appear anywhere in the document

/tr at end means, get the tr node of the matching element.

You dont need to extract each attribute one by one. Just get the entire node containing all 4 attributes in nokogiri, and get the attributes using:

theNode['href']
theNode['src']

where theNode is your Nokogiri Node object.

Edit: Sorry I haven't used these libraries, but I think the xpath evaluation and parsing is being done by mechanize. So here's how you would get the entire element and it's attributes in one go.

doc.xpath("td[3]/div[1]/a").each do |anchor|
    puts anchor['href']
    puts anchor['src']
    ...
end

Answer 3

FireXPath is highly recommended for quickly testing out/tweaking xpaths like this.

Answer 4

XPather for Firefox is by far the easiest tool to extract the xpath from an element.

[https://addons.mozilla.org/en-US/firefox/addon/1192]