Why doesn't this add the QObject* in QVector<QObject*>

Question

I've two ViewModels, MainVM and AddVM. In main.cpp, MainVM is declared this way:

MainVM *mvm;    
int main(int argc, char *argv[])
{
    ...
    mvm = new MainVM();
    ...
    engine.rootContext()->setContextProperty("mainContext", mvm);
    engine.rootContext()->setContextProperty("addContext", new AddVM());
    ...
}

and in MainVM, I've this Q_PROPERTY:

class MainVM : public QObject
{
    Q_OBJECT
    ...
    PROPERTY(QVector<Plot*>, plots)
    ...
public:
    ...
    QSqlDatabase db;
    int maxPlotId, maxSpaceId, maxTenantId, maxHeadId, maxLeaseId;
    ...
};

the PROPERTY macro does this:

#define PROPERTY(QType, name) \
    Q_PROPERTY(QType name READ name WRITE set##name NOTIFY name##Changed) \
    public: \
        QType name(){return m_##name;} \
        void set##name(QType value){if(m_##name != value){m_##name = value; emit name##Changed();}} \
        Q_SIGNAL void name##Changed(); \
    private: \
        QType m_##name;

In my AddVM I've another Q_PROPERTY newPlot and a Q_INVOKABLE addNewPlot:

class AddVM : public QObject
{
    Q_OBJECT
    PROPERTY(Plot*, newPlot)
public:
    explicit AddVM(QObject *parent = nullptr);
    Q_INVOKABLE void addNewPlot();
}; 

on top of the AddVM.cpp, I've these:

#include "MainVM.h"
extern MainVM *mvm;

and addNewPlot function has these instructions:

void AddVM::addNewPlot()
{
    mvm->db.open();
    QSqlQuery query;
    query.prepare("INSERT INTO Plots (Name, Description) VALUES(:Name, :Description)");
    query.bindValue(":Name", newPlot()->name());
    query.bindValue(":Description", newPlot()->description());
    query.exec();
    mvm->db.close();

    mvm->plots().push_back(newPlot());
    setnewPlot(new Plot());
    newPlot()->setid(++mvm->maxPlotId);
}

everything in this function works as expected except the mvm->plots().push_back(newPlot()); line! This doesn't add the newPlot in the QVector of MainVM!

EDIT

Probably the best way is to redefine the getter in the macro like this:

QType& name(){return m_##name;} \

and with that my existing code works without any modification.

Answer 1

When you call mvm->plots(), it returns a copy of the real plots vector (That's my guess because you didn't show what plots() does). Thus, a new plot is added to the copy not the original vector. So, I think the best way is to add a function in MainVM that is called 'addPlot()` for example where you can add to the plots vector internally and directly.