Hi, some days ago I posed the question on how could I resolve a Xpath expression using Xerces (XpathEvaluator class if I am not wrong).
Could someone give a little explanation on how it is done? I am searching everywhere for samples but cannot get one. (Already tried pathan code) I am not worried if results are given read-only. Thanks ! jima >> I'm writing about using XML in C++, and am briefly covering Xerces and > Xalan. >> I'd like to show an example of selecting a DOM node using an XPath > expression >> and then removing that node from the document. Unfortunately, while I've > found >> several ways to use XPath expressions to select a DOM node, they seem to > return >> nodes from a read-only view of the document. When I try to do >> >> node->getParentNode()->removeChild(node) >> >> I get an exception stating that the document is non-modifiable. > > Yes, the default implementation is read-only, since it's optimized for > XSLT, which does not allow modification of the source tree. > >> Is there a way to do what I'm trying to do using Xalan? If not, what's > another >> simple but non-trivial use of Xalan XPath expressions, outside of a > stylesheet? > > This is a pretty common question, and we should probably do a sample to > illustrate how it's done. You can search the mailing list archives of > both xalan-dev and xalan-c-users for "XercesDOMSupport" for more > information. > > The trick is you should use an instance of XercesParserLiaison instead of > XalanSourceTreeParserLiaison, and an instance of XercesDOMSupport, instead > of XalanSourceTreeDOMSupport. Also, you will need to call > XercesParserLiaison::setBuildWrapperNodes(true) and > XercesParserLiaison::setBuildMaps(true). Once you do that, you can call > XercesParserLiaison::parseXMLStream() and use the returned XalanDocument > instance as the source tree for evaluating XPath expressions. > > To map the resulting XalanNode instance returned from evaluating an XPath > expression, you first need to recover a pointer to the underlying > implementation class by calling XercesParserLiaison:: > mapDocumentToWrapper(). The implementation class XercesDocumentWrapper > has some member functions called mapNode() that will map the XalanNode > instances to their underlying Xerces DOMNode instances. You can then > manipulate the Xerces DOM instance as you wish. However, once you've > modified the underlying Xerces DOM instance, the existing Xalan wrapper > will be invalid, and you cannot use either the wrapper or the underlying > Xerces DOM instance for another XPath evaluation. If you want to preserve > the underlying Xerces DOM implementation, you can create it using the > standard Xerces-C APIs, then simply wrap it using XercesParserLiaison:: > createDocument(), rather than using XercesParserLiaison::parseXMLStream(). > > If it seems complicated, it's meant to be. Much of the XPath and XSLT > code assumes the underlying source tree will never be modified, so > providing a way to wrap the Xerces DOM and allow manipulating it is not > core functionality and can open up some dangerous holes. Proceed with > caution... > > Dave >
