QtMapStream - serialization of object class to QVariantMap.

[benlau]

Hi,

If you need to convert a lots of you own non-QObject based class to XML/YAML/JSON etc. You may be interested with my tiny project - QtMapStream.

Source code:
https://gitorious.org/qtmapstream/qtmapstream#more

QVariantMap is a synonym of QMap<QString, QVariant>. It could represent any complex objects. Convert
a QVariantMap instance to data serialization formats like XML , JSON and YAML is much easier than
a complex objects in C++. However, convert a C++ class to QVariantMap is not strict forward. User
have to implements their own convertion function.

The QtMapStream provides an interface and utility to convert user's own C++ class , which is not based
on QObject , to QVariantMap and vice versa.

Example class:

class Book {
 public:
    QString title;
    int pages;
    qreal rating;
 }

class Book {
 public:
    QString title;
    int pages;
    qreal rating;
 }

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You should add the QT_MAP_STREAMABLE / QT_MAP_STREAMABLE_ITEM macro to the class declaration:

class Book {
 public:
    QString title;
    int pages;
    qreal rating;
 
    QT_MAP_STREAMABLE(
        QT_MAP_STREAMABLE_ITEM(QString,title)
        QT_MAP_STREAMABLE_ITEM(int,pages)
        QT_MAP_STREAMABLE_ITEM(qreal,rating)
    )
 };

class Book {
 public:
    QString title;
    int pages;
    qreal rating;

    QT_MAP_STREAMABLE(
        QT_MAP_STREAMABLE_ITEM(QString,title)
        QT_MAP_STREAMABLE_ITEM(int,pages)
        QT_MAP_STREAMABLE_ITEM(qreal,rating)
    )
 };

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The macro will add <<,>> operators overloading with taking a QtMapStream to the class.

Convert to QVariantMap

Book book;
 book.title = "Qt Developer Guides";
 book.pages = 180;
 book.rating = 10.0;
 
 QtMapStream stream;
 book >> stream;
 
 QVariantMap source = stream.source(); // It will return the QVariantMap writen by the book instance.
 
 qDebug() << source; // QMap(("pages", QVariant(int, 180) ) ( "rating" ,  QVariant(double, 10) ) ( "title" ,  QVariant(QString, "Qt Developer Guides") ) )

Book book;
 book.title = "Qt Developer Guides";
 book.pages = 180;
 book.rating = 10.0;

 QtMapStream stream;
 book >> stream;

 QVariantMap source = stream.source(); // It will return the QVariantMap writen by the book instance.

 qDebug() << source; // QMap(("pages", QVariant(int, 180) ) ( "rating" ,  QVariant(double, 10) ) ( "title" ,  QVariant(QString, "Qt Developer Guides") ) )

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Convert from QVariantMap

Book book;
 QVariantMap map;
 map["title"] = "Qt Developer Guides";
 map["pages"] = 180;
 map["rating"] = 10.0;
 
 QtMapStream stream(map);
 book << stream; // The book instance will be filled with the information in QVariantmap
 
 QVariantMap remaining = stream.source(); // After run the << stream operators, written field will be removed from the source. Call source() should return an empty map.

Book book;
 QVariantMap map;
 map["title"] = "Qt Developer Guides";
 map["pages"] = 180;
 map["rating"] = 10.0;

 QtMapStream stream(map);
 book << stream; // The book instance will be filled with the information in QVariantmap

 QVariantMap remaining = stream.source(); // After run the << stream operators, written field will be removed from the source. Call source() should return an empty map.

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QtMapStream also support QList type. However, QList type can not be converted to QVariant directly. You should declare the QList type with Q_DECLARE_METATYPE first.

Example:

Q_DECLARE_METATYPE(QList<QString>)
 
 class BookV2 {
 public:
    QString title;
    int pages;
    qreal rating;
    QList<QString> authors;
 
    QT_MAP_STREAMABLE(
        QT_MAP_STREAMABLE_ITEM(QString,title)
        QT_MAP_STREAMABLE_ITEM(int,pages)
        QT_MAP_STREAMABLE_ITEM(qreal,rating)
        QT_MAP_STREAMABLE_ITEM(QList<QString> ,authors)
    )
 };

Q_DECLARE_METATYPE(QList<QString>)

 class BookV2 {
 public:
    QString title;
    int pages;
    qreal rating;
    QList<QString> authors;

    QT_MAP_STREAMABLE(
        QT_MAP_STREAMABLE_ITEM(QString,title)
        QT_MAP_STREAMABLE_ITEM(int,pages)
        QT_MAP_STREAMABLE_ITEM(qreal,rating)
        QT_MAP_STREAMABLE_ITEM(QList<QString> ,authors)
    )
 };

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Author : Ben Lau
License: New BSD