QSerializer: Lösung für die einfache JSON / XML-Serialisierung

Hintergrund

Bei der Serialisierung wird eine Datenstruktur in eine Folge von Bits übersetzt. Die Umkehrung der Serialisierungsoperation ist die Deserialisierungsoperation (Strukturierungsoperation) - die Wiederherstellung des Anfangszustands der Datenstruktur aus einer Bitsequenz.

QSerializer-Projektstruktur

Felddeklaration

class User : public QObject
{
Q_OBJECT
// Define data members to be serialized
Q_PROPERTY(QString name MEMBER name USER true)
Q_PROPERTY(int age MEMBER age USER true)
Q_PROPERTY(QString email MEMBER email USER true)
Q_PROPERTY(std::vector<QString> phone MEMBER phone USER true)
Q_PROPERTY(bool vacation MEMBER vacation USER true)
public:
  // Make base constructor
  User() { }
 
  QString name;
  int age{0};
  QString email;
  bool vacation{false};
  std::vector<QString> phone; 
};

#define QS_METATYPE(Type) qRegisterMetaType<Type>(#Type) ;
#define QS_REGISTER(Type)       \
QS_METATYPE(Type)               \
QS_METATYPE(Type*)              \
QS_METATYPE(std::vector<Type*>) \
QS_METATYPE(std::vector<Type>)  \

class User;
void main()
{
// define user-type in Qt meta-object system
QS_REGISTER(User)
...
}

QSerializer-Namespace

User u;
u.name = "Mike";
u.age = 25;
u.email = "example@exmail.com";
u.phone.push_back("+12345678989");
u.phone.push_back("+98765432121");
u.vacation = true;
QJsonObject json = QSerializer::toJson(&u);

{
    "name": "Mike",
    "age": 25,
    "email": "example@exmail.com",
    "phone": [
        "+12345678989",
        "+98765432121"
    ],
    "vacation": true
}

• Wenn Sie ein Objekt ändern müssen

  User u;
  QJsonObject userJson;
  QSerializer::fromJson(&u, userJson);

• Wenn Sie ein neues Objekt benötigen

  QJsonObject userJson;
  User * u = QSerializer::fromJson<User>(userJson);

Bewahrer

• QMetaSimpleKeeper - Property Keeper mit primitiven Datentypen
• QMetaArrayKeeper - Property Keeper mit Arrays primitiver Daten
• QMetaObjectKeeper - Bewahrer verschachtelter Objekte
• QMetaObjectArrayKeeper - Verwalter von Arrays verschachtelter Objekte

QMetaProperty prop;
QObject * linkedObj;
...
std::pair<QString, QJsonValue> QMetaSimpleKeeper::toJson()
{
    QJsonValue result = QJsonValue::fromVariant(prop.read(linkedObj));
    return std::make_pair(QString(prop.name()), result);
}

void QMetaSimpleKeeper::fromJson(const QJsonValue &val)
{
    prop.write(linkedObj, QVariant(val));
}

QMetaProperty prop;
QObject * linkedObj;
...
void QMetaObjectKeeper::fromJson(const QJsonValue &json)
{
    ...
    QSerializer::fromJson(linkedObj, json.toObject());
}

std::pair<QString, QJsonValue> QMetaObjectKeeper::toJson()
{
    QJsonObject result = QSerializer::toJson(linkedObj);;
    return std::make_pair(prop.name(),QJsonValue(result));
}

class PropertyKeeper
{
public:
    virtual ~PropertyKeeper() = default;
    virtual std::pair<QString, QJsonValue> toJson() = 0;
    virtual void fromJson(const QJsonValue&) = 0;
    virtual std::pair<QString, QDomNode> toXml() = 0;
    virtual void fromXml(const QDomNode &) = 0;
};

Wächterfabrik

    const std::vector<int> simple_t =
    {
        qMetaTypeId<int>(),
        qMetaTypeId<bool>(),
        qMetaTypeId<double>(),
        qMetaTypeId<QString>(),
    };

    const std::vector<int> array_of_simple_t =
    {
        qMetaTypeId<std::vector<int>>(),
        qMetaTypeId<std::vector<bool>>(),
        qMetaTypeId<std::vector<double>>(),
        qMetaTypeId<std::vector<QString>>(),
    };
...
PropertyKeeper *KeepersFactory::getMetaKeeper(QObject *obj, QMetaProperty prop)
{
    int t_id = QMetaType::type(prop.typeName());
    if(std::find(simple_t.begin(), simple_t.end(), t_id) != simple_t.end())
        return new QMetaSimpleKeeper(obj,prop);
    else if (std::find(array_of_simple_t.begin(),array_of_simple_t.end(), t_id) != array_of_simple_t.end())
    {
        if( t_id == qMetaTypeId<std::vector<int>>())
            return new QMetaArrayKeeper<int>(obj, prop);

        else if(t_id == qMetaTypeId<std::vector<QString>>())
            return new QMetaArrayKeeper<QString>(obj, prop);

        else if(t_id == qMetaTypeId<std::vector<double>>())
            return new QMetaArrayKeeper<double>(obj, prop);

        else if(t_id == qMetaTypeId<std::vector<bool>>())
            return new QMetaArrayKeeper<bool>(obj, prop);
    }
    else
    {
        QObject * castobj = qvariant_cast<QObject *>(prop.read(obj));
        if(castobj)
            return new QMetaObjectKeeper(castobj,prop);
        else if (QString(prop.typeName()).contains("std::vector<"))
        {
            QString t = QString(prop.typeName()).remove("std::vector<").remove(">");
            int idOfElement = QMetaType::type(t.toStdString().c_str());
            if(QMetaType::typeFlags(idOfElement).testFlag(QMetaType::PointerToQObject))
                return new QMetaObjectArrayKeeper(obj, prop);
        }
    }
    throw QSException(UnsupportedPropertyType);
}

std::vector<PropertyKeeper *> KeepersFactory::getMetaKeepers(QObject *obj)
{
    std::vector<PropertyKeeper*> keepers;
    for(int i = 0; i < obj->metaObject()->propertyCount(); i++)
    {
        if(obj->metaObject()->property(i).isUser(obj))
            keepers.push_back(getMetaKeeper(obj, obj->metaObject()->property(i)));
    }
    return keepers;
}
...

Einschränkungen und Verhalten