Extracting child node values with QXmlItem as a QXmlQuery focus

Question

I've been trying to fetch node text values from this XML file:

  <!DOCTYPE structure>
  <data>
   <x>
    <id>1</id>
    <nam>tytuł</nam>
    <tab>21</tab>
    <ind>5</ind>
    <pre>TY</pre>
    <khw>C.TY</khw>
   </x>
   <x>
    <id>2</id>
    <nam>autor</nam>
    <tab>21</tab>
    <ind>5</ind>
    <pre>FO</pre>
    <khw>C.FO</khw>
   </x>
   <x>
    <id>3</id>
    <nam>hasło korporatywne</nam>
    <tab>21</tab>
    <ind>5</ind>
    <pre>FN</pre>
    <khw>C.FN</khw>
   </x>
  </data>

What I want to do is to fetch every node and it's children and convert it to QMap. I have no trouble with fetching single element, but when it comes to fetch children items by setting result of QXmlQuery as a focus, the QString that i evaluate the child node query is empty. I use this piece of code:

QXmlResultItems results;
QFile structure("./structure.xml"); // xml file, as described earlier
structure.open(QFile::ReadOnly);

QXmlQuery query;
query.setFocus(&structure);
query.setQuery("data/x");
query.evaluateTo(&results);

QXmlItem next = results.next();
while(!next.isNull()) {
    qDebug() << next.toNodeModelIndex().stringValue(); // everything's fine. It prints contents of <x>'s child nodes
    QXmlQuery childQuery;
    QString r;
    childQuery.setFocus(next);
    childQuery.setQuery("./nam/text()"); // already tested: "/nam/text()", "/nam/string()", "x/nam/string()", "data/x/nam/string()" etc... still no luck.
    childQuery.evaluateTo(&r);
    qDebug() << r; // prints \n but it should print content of <nam> node.

    next = results.next();
}

Software I use: Qt 4.7.2 SDK directly from Qt website, QtCreator 2.3.1 on Windows and Linux (without any difference in this particular case, results are the same). I want to be sure that's the problem of my lack of knowledge, rather than software bug, please help

Answer 1

Unfortunately, it is unclear from Qt Documentation that in cases when you want to use QXmlQuery::setFocus(const QXmlItem& item) overload in order to query child nodes, you should create corresponding QXmlQuery objects using QXmlQuery(const QXmlNamePool& np) constructor to make them share the same QXmlNamePool object. Such sharing, simply speaking, relates queries to each other.

Considering this, your example should look like following:

QFile structure("./structure.xml");
structure.open(QFile::ReadOnly);

QXmlQuery query;
query.setFocus(&structure);
query.setQuery("data/x");

QXmlResultItems results;
query.evaluateTo(&results);

QXmlQuery childQuery(query.namePool());
while (!results.next().isNull()) {
    childQuery.setFocus(results.current());
    childQuery.setQuery("nam/text()");
    QString r;
    childQuery.evaluateTo(&r);
    qDebug() << r;
}

Moreover, you can go further and reuse initial QXmlQuery object:

QFile structure("./structure.xml");
structure.open(QFile::ReadOnly);

QXmlQuery query;
query.setFocus(&structure);
query.setQuery("data/x");

QXmlResultItems results;
query.evaluateTo(&results);

while (!results.next().isNull()) {
    query.setFocus(results.current());
    query.setQuery("nam/text()");
    QString r;
    query.evaluateTo(&r);
    qDebug() << r;
}

Answer 2

Instead of using evaluateTo( QString * ) use the QStringList version. It should work.