How to use xmlns declarations with XPath in Nokogiri

Question

I'm using Nokogiri::XML to parse responses from Amazon SimpleDB. The response is something like:

<SelectResponse xmlns="http://sdb.amazonaws.com/doc/2007-11-07/">
  <SelectResult>
    <Item>
      <Attribute><Name>Foo</Name><Value>42</Value></Attribute>
      <Attribute><Name>Bar</Name><Value>XYZ</Value></Attribute>
    </Item>
  </SelectResult>
</SelectResponse>

If I just hand the response straight over to Nokogiri, all XPath queries (e.g. doc/"//Item/Attribute[Name='Foo']/Value") return an empty array. But if I remove the xmlns attribute from the SelectResponse tag, it works perfectly.

Is there some extra thing I need to do to account for the namespace declaration? This workaround feels horribly like a hack.

score 32 · Accepted Answer · edited Dec 24 '19 at 21:51

32

That XPath query looks for elements that are not in any namespace. You need to tell your XPath processor that you are looking for elements in the http://sdb.amazonaws.com/doc/2007-11-07/ namespace.

One way to do that with Nokogiri is:

doc = Nokogiri::XML.parse(...)
doc.xpath("//aws:Item/aws:Attribute[Name='Foo']/aws:Value", {"aws" => "http://sdb.amazonaws.com/doc/2007-11-07/"})

edited Dec 24 '19 at 21:51

the Tin Man

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answered Nov 15 '09 at 14:04

hrnt

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Just providing "**xmlns:**" like `doc.xpath('//xmlns:Item...` should be working too. – user569825 Mar 19 '13 at 14:49

score 20 · Answer 2 · edited Dec 24 '19 at 21:54

20

I found "Namespaces in XML" really helpful in understanding what's going on.

Basically if you have a namespace defined via xmlns=, you must use a namespace in your XPath searches.

So in your case, you could do one of three things:

Remove the xmlns attribute from the root SearchResponse. In that case your original, namespace-less XPath query will work.

Use the default namespace in your XPath query:

doc/"//xmlns:Item/xmlns:Attribute[xmlns:Name='Foo']/xmlns:Value"

Define a custom namespace in the second argument of the xpath method and use that in your query, as shown in hrnt's solution above.

edited Dec 24 '19 at 21:54

the Tin Man

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answered May 10 '10 at 17:36

Matt Zukowski

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There's a `remove_namespaces!` method [documented here](http://nokogiri.org/Nokogiri/XML/Document.html#method-i-remove_namespaces%21). – RobinGower Oct 04 '11 at 22:17
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@RobinGower Yes, and it says `For more information on why this probably is not a good thing in general, please direct your browser to` [tenderlovemaking.com/2009/04/23/namespaces-in-xml/](http://tenderlovemaking.com/2009/04/23/namespaces-in-xml) – nurettin Jul 16 '12 at 12:14
Both the links in the comments are outdated. Here's an updated doc link for [remove_namespaces!](http://www.rubydoc.info/github/sparklemotion/nokogiri/Nokogiri/XML/Document:remove_namespaces!) – Jason Jul 29 '15 at 17:38

How to use xmlns declarations with XPath in Nokogiri

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