Adding/removing specific elements from xml file, in Qt? - c++

Question

I have a XML Document, like this:
<?xml version="1.0" encoding="UTF-8"?>
<items>
<item s_no="1">
<title>title_1</title>
<path>path1</path>
<desc>descriptoion1</desc>
</item>
<item s_no="2">
<title>title_2</title>
<path>path2</path>
<desc>descriptoion2</desc>
</item>
This is generated from QXmlStreamWriter in Qt. I want a function to add <item> tag with all elements like <title>, <path> etc. and I want a function to remove an item tag by identifying s_no attributes. All this should be done, without affecting any other content in the file.
I've searched a lot,I know there are similar questions, I've tried some code but it didn't worked. Are there any functions that do this, in QDomDocument?

Answer 1

When I have looked into doing this in the past, it hasn't really been a trivial thing.
QDomDocument and QDomNode
I think you should be able to do it with QDomDocument and QDomNode. Sometimes it is hard to see all the possible functions just on the main page for the documentation of the class, because it can get so much from the abstract classes it is derived from... clicking "lists of all members" shows a complete list.
http://doc.qt.io/qt-5/qdomdocument-members.html
Some calls that look promising include: childNodes elementById elementsByTagName createNode insertBefore insertAfter removeChild.
UPDATE: A working example that shows a straight forward way how to delete and insert nodes on a QDomDocument.
https://github.com/peteristhegreat/xml_insert_remove
Note, that when adding QDomNodes/QDomElements, etc, every element needs to be created on the document, otherwise it doesn't stay in scope when you leave a function.
QXmlStreamReader and QXmlStreamWriter
A few documents I've seen (a few years ago) said that they highly recommend using the QXmlStream* classes since they are better supported, or have been maintained more recently. I think it has some better error handling and doesn't have to load the whole document to be useful.
So as far as editing the document and resaving it, the most direct way that I know of is to read in everything, and store it as nested C++ classes and then write them out.
QJson Example (similar to QXmlStream*
There is a similar example with Json, that really shows off the power of subclassing a read and a write function into your model.
http://doc.qt.io/qt-5/qtcore-json-savegame-example.html
I think a similar approach could be done with the stream reader and writer class for XML.
Hope that helps.