Evaluating XPath expressions on a Xerces DOM

[AS...@desknetinc.com]

Hi all,

I am trying to write some software that will use Xalan to evaluate XPath
expressions, but my XML is represented in a Xerces DOM tree.  It works
under some circumstances but not others; particularly, I am having trouble
constructing a mapping between Xalan nodes and Xerces nodes.

Here's a generalized snippet from my code:

doc is a DOM_Document, and xmlNode is a DOM_Node

// Set up a XercesParserLiaison and use it to wrap the DOM_Document
// in a XalanDocument.
XercesDOMSupport theDOMSupport;
XercesParserLiaison theParserLiaison(theDOMSupport);
XalanDocument* theDocument = theParserLiaison.createDocument(doc);

if (theDocument == NULL)
      throw Exception("CannotCreateDocument");

XalanNode* theContextNode;
XercesDocumentBridge theBridge(doc);
XercesBridgeNavigator nav(&theBridge);

XPathEvaluator theEvaluator;

// OK, let's find the context node...
if (noContext)
{
      theContextNode = theDocument->getDocumentElement();
}
else
{
      theContextNode = nav.mapNode(xmlNode);
      if (theContextNode == NULL)
            throw Exception("InvalidContextNode");
}

If I haven't supplied a context node, it evaluates just fine (I'm passing
in one of the sample XPath expressions, and importing the foo.xml into a
Xerces DOM, and I get the expected result).  However, if I try to supply
the root node (as a DOM_Node) of foo.xml as the context node, it throws the
Invalid Context Node expression.  I've tried it just using
theBridge.mapNode(), and I also tried creating a navigator as you see here.
There doesn't seem to be much in the API docs to explain how these things
are all supposed to work, so I was hoping someone here had some experience
with this that they would like to share.  Thanks!

______________________________________
Aaron Scifres
Software Engineer
DeskNet, Inc.
66 Pearl St. Suite 300
Portland, ME 04101
(207) 772-1484 x16
http://www.desknetinc.com
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