Nokogiri: apply class to element that has a certain descendant - ruby

Question

Let's say I have this html that has various depths of descendants and a mixture of element types:
<div class="foo">
<div class="bar"></div>
</div>
<div class="foo">
<div class="baz"></div>
</div>
<div class="foo">
<u><span class="duh">
<div class="bar"></div>
</span></u>
</div>
<div class="foo">
<div class="baz"></div>
</div>
And I want to apply a class of bex to all the foos that contain classes of bar so it looks like:
<div class="bex">
<div class="bar"></div>
</div>
<div class="foo">
<div class="baz"></div>
</div>
<div class="bex">
<u><span class="duh">
<div class="bar"></div>
</span></u>
</div>
<div class="foo">
<div class="baz"></div>
</div>
How wld I do that with ruby/nokogiri? Tried all sorts of things and can't quite get it. Thanks.
Edit: closed the duh, oops.

Answer 1

I spent a long time wondering why the second foo wasn't found.
Your data is broken, "duh isn't closed.
To select the nodes, you can use :
doc.xpath("//div[#class='foo' and .//div[#class='bar']]")
As an example :
data = %q(<div class="foo">
<div class="bar"></div>
</div>
<div class="foo">
<div class="baz"></div>
</div>
<div class="foo">
<u><span class="duh">
<div class="bar"></div>
</span></u>
</div>
<div class="foo">
<div class="baz"></div>
</div>)
require 'nokogiri'
doc = Nokogiri.HTML(data)
doc.xpath("//div[#class='foo' and .//div[#class='bar']]").each do |node|
node["class"] = 'bex'
end
puts doc