CODEWITHSUNDEEP
c++jsonqt
eklavay.tonoy
eklavay.tonoy

Reputation: 23

QJson data serialization order

I have implemented a code that will take input from QLineEdit and the data will be saved in a json file format. 

void MainWindow::fileWriteOperationJson()
{    
    QString filename = "C:/Users/.../Documents/Qt/save.json";
    QFile saveFile(filename);
    saveFile.open(QIODevice::WriteOnly|QIODevice::Text);

    if (!saveFile.open(QIODevice::WriteOnly))
    {
          qWarning("Couldn't open save file.");    
    }

    QJsonObject obj; //this is the root
    QJsonArray personalData;    

    QJsonObject json;
    json["name"] = ui->nameLineEdit->text();
    json["address"] = ui->addressLineEdit->toPlainText();

    personalData.append(json);
    obj["personalData"] = personalData;

    QTextStream out(&saveFile);

    out << QJsonDocument(obj).toJson(QJsonDocument::Indented);    

}

Problem: When I open the json file, I want to find my data in the below format:

"name" = xyz
"address" = xyz

But, I am having result like this,

"address" = xyz
"name" = xyz

How to get this intended order?

Upvotes: 2

Views: 5468

Answers (3)

kcrossen
kcrossen

Reputation: 169

The underlying problem is that QMap does not have an ordered form. Here's a possible solution by subclassing QVariantMap:

#ifndef ORDEREDVARIANTMAP_H
#define ORDEREDVARIANTMAP_H

#include <QtCore>

class OrderedVariantMap : public QMap<QString, QVariant> {
// Test:
//    OrderedVariantMap test_map;
//    test_map.insert("xxx", 1);
//    test_map.insert("aaa", 2);
//    test_map.insert("kkk", 3);

//    test_map["321"] = 4;
//    test_map["000"] = 5;
//    test_map["123"] = 6;

//    qDebug() << "QMap.keys()" << test_map.keys();
//    qDebug() << "QMap.orderedKeys()" << test_map.orderedKeys();

//    QVariant test_variant;
//    test_variant.setValue(test_map);
//    qDebug() << "test_variant.typeName()" << test_variant.typeName();
//    OrderedVariantMap test_map_recovered = qvariant_cast<OrderedVariantMap>(test_variant);
//    qDebug() << "test_map_recovered.orderedKeys()" << test_map_recovered.orderedKeys();

// Test results:
//    QMap.keys() ("000", "123", "321", "aaa", "kkk", "xxx")
//    QMap.orderedKeys() ("xxx", "aaa", "kkk", "321", "000", "123")
//    test_variant.typeName() OrderedVariantMap
//    test_map_recovered.orderedKeys() ("xxx", "aaa", "kkk", "321", "000", "123")

public:
    OrderedVariantMap ( );
    ~OrderedVariantMap ( );

void
clear ( );

void // QMap::iterator
insert ( const QString &key,
         const QVariant &value );

QVariant&
operator[] ( const QString &key );

const QVariant
operator[] ( const QString &key ) const;

const QString
orderedKey ( int index ) const;

const QVariant
orderedValue ( int index ) const;

QStringList
orderedKeys ( ) const ;

private:
    QStringList Ordered_Keys;

protected:

};

Q_DECLARE_METATYPE(OrderedVariantMap)

#endif // ORDEREDVARIANTMAP_H

and

#include "OrderedVariantMap.h"

OrderedVariantMap::OrderedVariantMap ( ) : QMap ( ) {

}

OrderedVariantMap::~OrderedVariantMap ( ) {

}

QStringList
OrderedVariantMap::orderedKeys ( ) const {
    return Ordered_Keys;
}

void
OrderedVariantMap::clear ( ) {
    Ordered_Keys.clear();
    QMap::clear();
}

void // QMap::iterator
OrderedVariantMap::insert ( const QString &key,
                            const QVariant &value ) {
    Ordered_Keys.append(key);
    QMap::insert(key, value);
}

QVariant&
OrderedVariantMap::operator[] ( const QString &key ) {
    Ordered_Keys.append(key);
    return QMap::operator [](key);
}

const QVariant
OrderedVariantMap::operator[] ( const QString &key ) const {
    return this->value(key);
}

const QString
OrderedVariantMap::orderedKey ( int index ) const {
    return Ordered_Keys[index];
}

const QVariant
OrderedVariantMap::orderedValue ( int index ) const {
    return this->value(Ordered_Keys[index]);
}

More functionality could be provided, for example an ordered iterator.

Upvotes: 2

owacoder
owacoder

Reputation: 4873

Qt generates JSON data with keys sorted alphabetically. AFAIK, there is no option to get around it. You could try encapsulating objects with a single key/value pair into an array, though, and preserve the order:

[
     {"address": xyz},
     {"name": xyz}
]

Or you could try using a different storage format altogether.

Upvotes: 3

TheDarkKnight
TheDarkKnight

Reputation: 27611

JSON (JavaScript Object Notation) is a lightweight data-interchange format and as such, the structure is important, but the order of items is not.

If you need to print the items in a specific order, you'll need to extract them from Json into suitable data structures and handle that yourself.

Alternatively, you could save to a different format, but note that Qt's XML will act the same as Json. Perhaps a CSV may be more useful to you.

Upvotes: 4

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