XML querying particular node from C#

Question

I have written a chunk of XML parsing which works successfully provided I use an absolute path.

I now need to take an XMLNode as an argument and run an xpath against this.

Does anyone know how to do this?

I tried using relative XPath queries without any success!!

Should it be this hard??

Answer 1

It would help to see examples of XPath expressions that don't work as you think they should. Here are some possible causes (mistakes I frequently make).

Assume an XML document such as:

<A>
  <B>
    <C d='e'/>
  </B>
  <C/>
  <D xmlns="http://foo"/&gt;
</A>

• forgetting to remove the top-level slash ('/') representing the document:

  document.XPathSelectElements("/A") // selects a single A node

  document.XPathSelectElements("//B") // selects a single B node

  document.XPathSelectElements("//C") // selects two C nodes

but

aNode.XPathSelectElements("/B") // selects nothing (this looks for a rootNode with name B)
aNode.XPathSelectElements("B") // selects a B node

bNode.XPathSelectElements("//C") // selects TWO C nodes - all descendants of the root node
bNode.select(".//C") // selects one C node - all descendants of B

• forgetting namespaces.

  aNode.XPathSelectElements("D") // selects nothing (D is in a different namespace from A) aNode.XPathSelectElements("[local-name()='D' and namespace-uri()='http://foo']") // one D node

(This is often a problem when the root node carries a prefixless namespace - easy to miss)