QXmlQuery update of attributes

[blgis]

I'm really new with the XQuery language. I try to update an attribute value in a XML document with XQuery an the QXmlQuery class.
I found the following example on the internet.

XML Source:

<root foo="bar">
    <message>Hello!</message>
</root>

XQuery Code:

let $doc := doc('/db/test/update-attribute/root.xml')/root

return update value $doc/@foo with 'new-value'

XML Result:

<root foo="new-value">
    <message>Hello!</message>
</root>

Is it possible to do this with QXmlQuery class?
I tried it with the following code, but it didn't work:

QString fileName("D:\\source.xml");
QFile file(fileName);
if (file.open(QIODevice::ReadOnly))
{
        QXmlQuery xmlQuery;
        xmlQuery.bindVariable("fileName", &file);
	
	QString resultString;
	QString queryString;
	queryString = "declare variable $fileName external;\n";
        queryString += "let $doc := doc($fileName)/root\n";
        queryString += "return update value $doc/@foo with 'new-value'\n";
	xmlQuery.setQuery(queryString);
        if (xmlQuery.evaluateTo(&resultString))
		qDebug() << resultString;
}

A Query like "declare variable $fileName external; doc($fileName)/root/@foo/data(.)" works, but update operation like described above not. Is update possible with QXmlQuery class or is a newer version of the XQuery language or an extenstion necessary which QXmlQuery don't support?

[AshkanV]

Hello
I had the same problem. It is looks like that Qt currently only supports "Minimal Conformance" and yet does not support optional XQuery features as it is described here:

QXMLQuery Features and Conformance:

XQuery 1.0

Qt XML Patterns aims at being a conformant XQuery processor. It adheres to Minimal Conformance and supports the Serialization Feature and the Full Axis Feature. Qt XML Patterns currently passes 97% of the tests in the XML Query Test Suite. Areas where conformance may be questionable and where behavior may be changed in future releases include:

Some corner cases involving namespaces and element constructors are incorrect.
XPath is a subset of XQuery and the implementation of Qt XML Patterns uses XPath 2.0 with XQuery 1.0.

The specifications discusses conformance further: XQuery 1.0: An XML Query Language. W3C's XQuery testing effort can be of interest as well, XML Query Test Suite.

Currently fn:collection() does not access any data set, and there is no API for providing data through the collection. As a result, evaluating fn:collection() returns the empty sequence. We intend to provide functionality for this in a future release of Qt.

Only queries encoded in UTF-8 are supported.

And here is the relation of XQuery update with "Minimal Conformance"

So I guess this feature is not included in the current version of QXMLQuery

Instead it is possible to use QDomDocument