How does XPath deal with XML namespaces?
How does XPath deal with XML namespaces?
If I use
/IntuitResponse/QueryResponse/Bill/Id
to parse the XML document below I get 0 nodes back.
<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<IntuitResponse xmlns="http://schema.intuit.com/finance/v3"
time="2016-10-14T10:48:39.109-07:00">
<QueryResponse startPosition="1" maxResults="79" totalCount="79">
<Bill domain="QBO" sparse="false">
<Id>=1</Id>
</Bill>
</QueryResponse>
</IntuitResponse>
However, I'm not specifying the namespace in the XPath (i.e. http://schema.intuit.com/finance/v3
is not a prefix of each token of the path). How can XPath know which Id
I want if I don't tell it explicitly? I suppose in this case (since there is only one namespace) XPath could get away with ignoring the xmlns
entirely. But if there are multiple namespaces, things could get ugly.
Solution 1:
Defining namespaces in XPath (recommended)
XPath itself doesn't have a way to bind a namespace prefix with a namespace. Such facilities are provided by the hosting library.
It is recommended that you use those facilities and define namespace prefixes that can then be used to qualify XML element and attribute names as necessary.
Here are some of the various mechanisms which XPath hosts provide for specifying namespace prefix bindings to namespace URIs.
(OP's original XPath, /IntuitResponse/QueryResponse/Bill/Id
, has been elided to /IntuitResponse/QueryResponse
.)
C#:
XmlNamespaceManager nsmgr = new XmlNamespaceManager(doc.NameTable);
nsmgr.AddNamespace("i", "http://schema.intuit.com/finance/v3");
XmlNodeList nodes = el.SelectNodes(@"/i:IntuitResponse/i:QueryResponse", nsmgr);
Java (SAX):
NamespaceSupport support = new NamespaceSupport();
support.pushContext();
support.declarePrefix("i", "http://schema.intuit.com/finance/v3");
Java (XPath):
xpath.setNamespaceContext(new NamespaceContext() {
public String getNamespaceURI(String prefix) {
switch (prefix) {
case "i": return "http://schema.intuit.com/finance/v3";
// ...
}
});
- Remember to call
DocumentBuilderFactory.setNamespaceAware(true)
. - See also: Java XPath: Queries with default namespace xmlns
JavaScript:
See Implementing a User Defined Namespace Resolver:
function nsResolver(prefix) {
var ns = {
'i' : 'http://schema.intuit.com/finance/v3'
};
return ns[prefix] || null;
}
document.evaluate( '/i:IntuitResponse/i:QueryResponse',
document, nsResolver, XPathResult.ANY_TYPE,
null );
Note that if the default namespace has an associated namespace prefix defined, using the nsResolver()
returned by Document.createNSResolver()
can obviate the need for a customer nsResolver()
.
Perl (LibXML):
my $xc = XML::LibXML::XPathContext->new($doc);
$xc->registerNs('i', 'http://schema.intuit.com/finance/v3');
my @nodes = $xc->findnodes('/i:IntuitResponse/i:QueryResponse');
Python (lxml):
from lxml import etree
f = StringIO('<IntuitResponse>...</IntuitResponse>')
doc = etree.parse(f)
r = doc.xpath('/i:IntuitResponse/i:QueryResponse',
namespaces={'i':'http://schema.intuit.com/finance/v3'})
Python (ElementTree):
namespaces = {'i': 'http://schema.intuit.com/finance/v3'}
root.findall('/i:IntuitResponse/i:QueryResponse', namespaces)
Python (Scrapy):
response.selector.register_namespace('i', 'http://schema.intuit.com/finance/v3')
response.xpath('/i:IntuitResponse/i:QueryResponse').getall()
PhP:
Adapted from @Tomalak's answer using DOMDocument:
$result = new DOMDocument();
$result->loadXML($xml);
$xpath = new DOMXpath($result);
$xpath->registerNamespace("i", "http://schema.intuit.com/finance/v3");
$result = $xpath->query("/i:IntuitResponse/i:QueryResponse");
See also @IMSoP's canonical Q/A on PHP SimpleXML namespaces.
Ruby (Nokogiri):
puts doc.xpath('/i:IntuitResponse/i:QueryResponse',
'i' => "http://schema.intuit.com/finance/v3")
Note that Nokogiri supports removal of namespaces,
doc.remove_namespaces!
but see the below warnings discouraging the defeating of XML namespaces.
VBA:
xmlNS = "xmlns:i='http://schema.intuit.com/finance/v3'"
doc.setProperty "SelectionNamespaces", xmlNS
Set queryResponseElement =doc.SelectSingleNode("/i:IntuitResponse/i:QueryResponse")
VB.NET:
xmlDoc = New XmlDocument()
xmlDoc.Load("file.xml")
nsmgr = New XmlNamespaceManager(New XmlNameTable())
nsmgr.AddNamespace("i", "http://schema.intuit.com/finance/v3");
nodes = xmlDoc.DocumentElement.SelectNodes("/i:IntuitResponse/i:QueryResponse",
nsmgr)
SoapUI (doc):
declare namespace i='http://schema.intuit.com/finance/v3';
/i:IntuitResponse/i:QueryResponse
xmlstarlet:
-N i="http://schema.intuit.com/finance/v3"
XSLT:
<xsl:stylesheet version="1.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
xmlns:i="http://schema.intuit.com/finance/v3">
...
Once you've declared a namespace prefix, your XPath can be written to use it:
/i:IntuitResponse/i:QueryResponse
Defeating namespaces in XPath (not recommended)
An alternative is to write predicates that test against local-name()
:
/*[local-name()='IntuitResponse']/*[local-name()='QueryResponse']
Or, in XPath 2.0:
/*:IntuitResponse/*:QueryResponse
Skirting namespaces in this manner works but is not recommended because it
-
Under-specifies the full element/attribute name.
-
Fails to differentiate between element/attribute names in different namespaces (the very purpose of namespaces). Note that this concern could be addressed by adding an additional predicate to check the namespace URI explicitly1:
/*[ namespace-uri()='http://schema.intuit.com/finance/v3' and local-name()='IntuitResponse'] /*[ namespace-uri()='http://schema.intuit.com/finance/v3' and local-name()='QueryResponse']
1Thanks to Daniel Haley for the
namespace-uri()
note. -
Is excessively verbose.
Solution 2:
I use /*[name()='...']
in a google sheet to fetch some counts from Wikidata. I have a table like this
thes WD prop links items
NOM P7749 3925 3789
AAT P1014 21157 20224
and the formulas in cols links
and items
are
=IMPORTXML("https://query.wikidata.org/sparql?query=SELECT(COUNT(*)as?c){?item wdt:"&$B14&"[]}","//*[name()='literal']")
=IMPORTXML("https://query.wikidata.org/sparql?query=SELECT(COUNT(distinct?item)as?c){?item wdt:"&$B14&"[]}","//*[name()='literal']")
respectively. The SPARQL query happens not to have any spaces...
I saw name()
used instead of local-name()
in Xml Namespace breaking my xpath!, and for some reason //*:literal
doesn't work.