How to update a node in xml using QStreamWritter class?

Sherlin N G · 2 Mar 2018, 08:50

I have an xml file in which i want to change the the attribute values of a node node.
how can i do it using QXmlStreamWritter class,

ex:if i want to change the value of <heading> from reminder to something without being appending the new node node to the xml file.

<note>
<to>Tove</to>
<from>kishore</from>
<heading>Reminder</heading>
<body>hi!</body>
</note>

jsulm · 3 Feb 2018, 08:52

@Sherlin-N-G I guess you mean QXmlStreamWritter?
Like shown here: http://doc.qt.io/qt-5/qxmlstreamwriter.html ?

QXmlStreamWriter stream(&output);
    stream.setAutoFormatting(true);
    stream.writeStartDocument();
    ...
    stream.writeStartElement("bookmark");
    stream.writeAttribute("href", "http://qt-project.org/"); // <----- HERE
    stream.writeTextElement("title", "Qt Project");
    stream.writeEndElement(); // bookmark
    ...
    stream.writeEndDocument();

Sherlin N G · 2 Mar 2018, 09:11

hi @jsulm

i think this will write the node again to the xml file,
i want to change the values of existing node attributes.

thank you for the reply

jsulm · 2 Mar 2018, 10:07

@Sherlin-N-G You can simply overwrite the whole XML document.

Sherlin N G · 2 Mar 2018, 10:32

@jsulm
hi
i have multiple note node inside my XML file , how can i add the set attribute value to particular node node.

JonB · 2 Mar 2018, 11:00

@Sherlin-N-G
You have to (search the document to) select the particular node you want to alter. You can sit inserting/deleting/updating nodes in an XML document for as long as you like. Then you write the complete XML document back to file when you're finished. That's the normal/simplest way of doing things in a whole XML document. Do you have a particular reason for wanting to go down to the QXmlStreamWriter level?

Sherlin N G · wrote on 2 Mar 2018, 10:43

hi @JonB i tried with code in the document , i am confused with these 2 line of code

stream.writeAttribute("href", "http://qt-project.org/"); // <----- HERE
stream.writeTextElement("title", "Qt Project");

No, i can use any class for over writing but i feel QXmlStreamWriter is easy to implement.

kishore_hemmady · 2 Mar 2018, 11:37

@JonB Hi
I dont think so you can read a node you want to alter and write simultaneously using DOM.

Sherlin N G · 2 Mar 2018, 11:38

this is my xml file in which i need to change the value of X_value from car to bus by the below code

this is my snippet to update a node attribute X_value
void MainWindow::on_pushButton_2_clicked()
{

  QString output("/something/newXml1.xml");
  QXmlStreamWriter stream(&output);
  stream.setAutoFormatting(true);
  stream.writeStartDocument();
  stream.writeStartElement("Note");
  stream.writeAttribute("href", "http://qt-project.org/"); // <----- HERE
  
  stream.writeTextElement("X_value", "Qt Project");
  stream.writeEndElement(); // Zone

 // stream.writeEndDocument();

}

please help in this.

JonB · wrote on 2 Mar 2018, 11:37

@kishore_hemmady said in How to update a node in xml using QStreamWritter class?:

@JonB Hi
I dont think so you can read a node you want to alter and write simultaneously using DOM.

I meant, read the whole doc into DOM, alter, write whole DOM back. For simplicity, personally I wouldn't be doing anything at the whole QXmlStreamWriter level. That's why I was asking whether the OP is wedded to that.

jsulm · wrote on 2 Mar 2018, 11:38

@Sherlin-N-G You can use http://doc.qt.io/qt-5/qdomdocument.html
Simply read your whole document, then alter it and write it back to the file.

Sherlin N G · 2 Mar 2018, 12:11

@jsulm

above code will not work for updating??
do i need to read from QDom and then write?

JonB · 3 Feb 2018, 12:12

@Sherlin-N-G
I do think you need to confirm whether you are happy to use QDomDocument level, as I and @jsulm are suggesting, or whether you actively wish to use QXmlStreamWriter? Which is what I have been asking.