Re: [xml] XPath/Document concurrency issue

[Belgabor <belgabor gmx de>]

Daniel Veillard schrieb:
> On Sat, Feb 23, 2008 at 03:05:27AM +0100, Belgabor wrote:
> > Hi everybody,
> >
> > I have a strange problem which I can only describe as a concurrency 
> > issue between the (xml) document content and the results I get from 
> > XPath queries. I'm working on a project where I plan to use the 
> > Model/Controller/View architecture, the model being a parsed xml tree 
> > and read/write access to it is mainly done via XPath queries. Therefore 
> > I'm quite worried by this issue.
> >
> > Here's what I do:
> >
> > - Read xml document
> > - Create an XPath context (xmlXPathNewContext)
> > - Run a query (xmlXPathEvalExpression), getting a result node
> > - Create a new node (xmlNewNode), set content (xmlEncodeSpecialChars, 
> > xmlNodeSetContent)
> > - Add new node as child to the result node (xmlAddChild)
> >
> > Later:
> > - Create an XPath context (xmlXPathNewContext) with the same document
> > - Run a query (xmlXPathEvalExpression) which checks for the content of 
> > the node added above in a predicate.
> > - Get no result.
> >
> > The curious thing is (and the reason why I bring it here rather than 
> > think it's an issue of the c++ wrapper around libxml2 I wrote) that 
> > after I save the document to disk and reload it, everything works as 
> > expected.
>
>   My guess is that when you modify the tree you build it wrong (I'm guessing
> you're using namespaces and not properly building your tree), the output
> once serialized looks fine, but the internal tree structures are wrong.
> That would lead to XPath failing on the modifed tree and but succeeding
> when serializing/parsing. Triple check all the pointers and namespaces
> generated when using xmlAddChild.

Right on the spot. Thanks a lot, works fine now =)