:first-child not working when selecting on .class

[morganchristiansson]

require 'rubygems'
require 'mechanize'

agent=Mechanize.new
agent.user_agent='wget' # default user-agent string is banned apparantly
page=agent.get('http://en.wikipedia.org/wiki/Comparison_of_file_archivers')

page.search('table.wikitable:first-child') #does not work
page.search('.wikitable:first-child')      #does not work
page.search('table:first-child')           #works - but it's not a .wikitable table
page.search('table.wikitable')             #works - returns 5 tables

The error is:

> page.search('table.wikitable:first-child')
RuntimeError: xmlXPathCompOpEval: function first-child not found
from /usr/lib/ruby/gems/1.8/gems/nokogiri-1.4.0/lib/nokogiri/xml/node.rb:142:in `evaluate'
from /usr/lib/ruby/gems/1.8/gems/nokogiri-1.4.0/lib/nokogiri/xml/node.rb:142:in `xpath'
from /usr/lib/ruby/gems/1.8/gems/nokogiri-1.4.0/lib/nokogiri/xml/node.rb:139:in `map'
from /usr/lib/ruby/gems/1.8/gems/nokogiri-1.4.0/lib/nokogiri/xml/node.rb:139:in `xpath'
from /usr/lib/ruby/gems/1.8/gems/nokogiri-1.4.0/lib/nokogiri/xml/node.rb:106:in `search'
from (irb):119
from /usr/local/lib/site_ruby/1.8/rubygems.rb:168

RuntimeError: xmlXPathCompOpEval: function first-child not found

  from /usr/lib/ruby/gems/1.8/gems/nokogiri-1.4.0/lib/nokogiri/xml/node.rb:142:in `evaluate'
  from /usr/lib/ruby/gems/1.8/gems/nokogiri-1.4.0/lib/nokogiri/xml/node.rb:142:in `xpath'
  from /usr/lib/ruby/gems/1.8/gems/nokogiri-1.4.0/lib/nokogiri/xml/node.rb:139:in `map'
  from /usr/lib/ruby/gems/1.8/gems/nokogiri-1.4.0/lib/nokogiri/xml/node.rb:139:in `xpath'
  from /usr/lib/ruby/gems/1.8/gems/nokogiri-1.4.0/lib/nokogiri/xml/node.rb:106:in `search'
  from (irb):119
  from /usr/local/lib/site_ruby/1.8/rubygems.rb:168

Using Mechanize 1.0.0.

[drbrain]

There is no table that has a class of 'wikitable' and is a first-child in that document.

Perhaps you mean 'table.wikitable :first-child' (the tbody).

[morganchristiansson]

Oh is that how it works. I think what I was after was the first matched element like page.search('xxx')[0] or LIMIT 1 in SQL.