why no findXmlElement functions?

[fryn3]

why no findXmlElement functions?

class MyXmlStreamReader : public QXmlStreamReader
{
public:
    MyXmlStreamReader() : QXmlStreamReader() { }
    MyXmlStreamReader(QIODevice *device) : QXmlStreamReader(device) { }
    MyXmlStreamReader(const QByteArray &data) : QXmlStreamReader(data) { }
    MyXmlStreamReader(const QString &data) : QXmlStreamReader(data) { }
    MyXmlStreamReader(const char * data) : QXmlStreamReader(data) { }
    bool findXmlElement(QStringList path) {
        if (path.isEmpty()) {
            return false;
        }
        QString findName = path.at(0);
        while (!atEnd() && !hasError()) {
            readNextStartElement();
            if (findName == name()) {
                if (path.size() == 1) {
                    return true;
                } else {
                    return findXmlElement(path.mid(1));
                }
            } else {
                skipCurrentElement();
            }
        }
        return false;
    }
    bool findXmlElement(QList<QRegExp> path) { return false; }   // not implemented
};

Example
xml-file

<?xml version="1.0" encoding="UTF-16" ?>
<persons>
    <person id="1">
        <firstname>John</firstname>
        <surname>Doe</surname>
        <email>john.doe@example.com</email>
        <website>http://en.wikipedia.org/wiki/John_Doe</website>
    </person>
    <person id="2">
        <firstname>Jane</firstname>
        <surname>Doe</surname>
        <email>jane.doe@example.com</email>
        <website>http://en.wikipedia.org/wiki/John_Doe</website>
    </person>
    <person id="3">
        <firstname>Matti</firstname>
        <surname>Meikäläinen</surname>
        <email>matti.meikalainen@example.com</email>
        <website>http://fi.wikipedia.org/wiki/Matti_Meikäläinen</website>
    </person>
</persons>

code

int main (int argc, char *argv[]) {
    QApplication a(argc, argv);
    QFile f("file.xml");
    f.open(QIODevice::ReadOnly);
    MyXmlStreamReader xml(&f);
    qDebug() << xml.findXmlElement(QStringList() << "persons" << "person" << "email");
    qDebug() << xml.tokenString() << xml.name() << xml.text();
    return 0;
}

[JonB]

@fryn3 said in why no findXmlElement functions?:

why no findXmlElement functions?

What sort of an answer are you expecting to this? QXmlStreamReader does not provide "find" functions, it's a forward-only fast stream reader. Use https://doc.qt.io/qt-5/qdomdocument.html (e.g. elementsByTagName()) if you want more advanced capabilities after reading in a whole document. Otherwise you are are writing your own findXmlElement() methods, so what's the issue?

[fryn3]

@JonB said in why no findXmlElement functions?:

Use https://doc.qt.io/qt-5/qdomdocument.html (e.g. elementsByTagName()) if you want more advanced capabilities after reading in a whole document.

The module is not actively maintained anymore. Please use the QXmlStreamReader and QXmlStreamWriter classes in Qt Core instead.

Later, I will prepare a detailed answer.

[VRonin]

efficiency point:

 bool findXmlElement(QStringList path){return findXmlElement(path.cbegin(),path.cend());}
private:
 bool findXmlElement(QStringList::const_iterator pathBegin,QStringList::const_iterator pathEnd) {
        if (pathBegin==pathEnd)
            return false;
        while (!atEnd() && !hasError()) {
            readNextStartElement();
            if (*pathBegin== name()) {
                if (++pathBegin == pathEnd)
                    return true;
                    return findXmlElement(pathBegin ,pathEnd);
            } else {
                skipCurrentElement();
            }
        }
        return false;
    }

Functionality point:
If you have

<person id="1">
        <firstname>John</firstname>
        <surname>Doe</surname>
        <email>john.doe@example.com</email>
        <website>http://en.wikipedia.org/wiki/John_Doe</website>
    </person>
    <person id="2">
        <firstname>Jane</firstname>
        <surname>Doe</surname>
       <middlename>James</middlename>
        <email>jane.doe@example.com</email>
        <website>http://en.wikipedia.org/wiki/John_Doe</website>
    </person>

Your algorithm will not be able to find QStringList{"person","middlename"}

[fryn3]

This post is deleted!

[JonB]

@fryn3

The module is not actively maintained anymore. Please use the QXmlStreamReader and QXmlStreamWriter classes in Qt Core instead.

I don't know if this is something aimed at me? Whatever link you put on "The module" in what you wrote doesn't lead anywhere?

[LeLev]

@JonB https://doc.qt.io/QT-5/qtxml-module.html

[JonB]

@LeLev
Oh! You mean that all those QXml... and QDom... classes are being withdrawn? No support for reading your entire XML document into a DOM and searching/editing it from there? Seriously? Seems like a retrograde step, Qt provides loads of useful stuff, does it not need such slightly higher-level support for XML?

[Christian Ehrlicher]

QtXml is in 'done' state - this doesn't mean it will be removed. It just will not gain any major updates anymore.

[VRonin]

Just to give you a comparison, bzip2 hasn't received a major update since 2010 and zlib hasn't received any update for more than2 years but they are still the most used compression libraries i can think of. The Qt xml module entered the same stage, it implemented all the features that were considered "in scope" and it woks well as is

[JonB]

Good to know. In which case, although the OP rejected my suggestion that he could choose to read the whole document in and do things like QDomDocument::elementsByTagName() because "The module is not actively maintained anymore", that is still an acceptable approach going forward, right?

[JonB]

BTW, I've just searched and am delighted to see that Qt does have XPath/XQuery, https://doc.qt.io/qt-5/xmlprocessing.html. It's up to the OP, but I will say that using XPath queries on your XML documents is an order of magnitude nicer than walking the tree in code.

And for quite separate purposes, I see that also has (at least some) XSLT support, so it gets better & better... :)