How to modify data and save to json file?

[Alex Dragon]

I loaded json file, shown it to listmodel and I want to save data in json file.
Help me!

[SGaist]

Hi,

What exactly did you implement ?

[sharath]

Hi @Alex-Dragon ,
You suppose to use QJsonValueReference to modify the json data.

{
    "FirstName": "John",
    "LastName": "Doe",
    "Age": 43,
    "Address": {
        "Street": "Downing Street 10",
        "City": "London",
        "Country": "Great Britain"
    },
    "Phone numbers": [
        "+44 1234567",
        "+44 2345678"
    ]
}

suppose now if you need to change the street name, use the following code.

QFile file(filepath);
file.open(QIODevice::ReadOnly | QIODevice::Text);
QJsonParseError JsonParseError;
QJsonDocument JsonDocument = QJsonDocument::fromJson(file.readAll(), &JsonParseError);
file.close();
QJsonObject RootObject = JsonDocument.object();
QJsonValueRef ref = RootObject.find("Address").value();
QJsonObject m_addvalue = ref.toObject();
m_addvalue.insert("Street","India");//set the value you want to modify
ref=m_addvalue; //assign the modified object to reference
JsonDocument.setObject(RootObject); // set to json document
file.open(QFile::WriteOnly | QFile::Text | QFile::Truncate);
file.write(JsonDocument.toJson());
file.close();

try this and let me know your result.
Happy coding.

[josht000]

@sharath Really awesome code snippet! Saved me lots of time, was exactly what I was looking for, and it worked great. Thanks!!!!

[Pablo J. Rogina]

@josht000 please don't forget to mark your post as solved!

[SGaist]

@Pablo-J-Rogina it's not the original author of this thread ;-)

[yashnikam]

How to add phone numbers in this code snippet?

[jsulm]

@yashnikam In the same way it is done for address...

[the woft]

@SGaist I want to change the value of FirstName and Age , it has no object to find , pls help me !

[JonB]

@the-woft
FirstName and Age are in the RootObject just like Address is. Their values will be a string and an integer respectively, so retrievable via QString QJsonValue::toString() const & int QJsonValue::toInt(int defaultValue = 0) const and modifiable via QJsonValueRef QJsonObject::operator[](const QString &key).

[the woft]

@JonB said in How to modify data and save to json file?:

FirstName and Age are in the RootObject just like Address is. Their values will be strings, so retrievable via QString QJsonValue::toString() const and modifiable via QJsonValueRef QJsonObject::operator[](const QString &key).

i'm newbie in qt and i try it but not correct , you can give me sample code do it ?

[jsulm]

@the-woft said in How to modify data and save to json file?:

and i try it but not correct

Then show what you tried.
There is example code in documentation and example applications like https://doc.qt.io/qt-6/qtcore-serialization-savegame-example.html

[the woft]

@jsulm this my code
QJsonValue Age = root_object.value("Age");
QVariant tmp = Age.toVariant();
qlonglong result = root_object.value("Age").toVariant().toLongLong();
QJsonValueRef ref = RootObject("result");
QJsonObject m_addvalue = ref.toObject();

[JonB]

@the-woft
You read the Age entry in root_object but where do you set the Age entry in root_object? You don't. I gave you the reference to QJsonValueRef QJsonObject::operator[](const QString &key) to use.

[the woft]

@JonB was exactly what I was looking for, and it worked great. Thanks!!!!

[JonB]

@the-woft For other readers you might post the line of code you added to set rootObject["Age"] correctly.