QSqlTableModel::editStrategy, QDataWidgetMapper and persistent model indexes

#include <QVBoxLayout>
#include <QMainWindow>
#include <QSqlDatabase>
#include <QMessageBox>
#include <QSqlQuery>
#include <QWidget>
#include <QApplication>
#include <QTableView>
#include <QSqlTableModel>
#include <QLineEdit>
#include <QLabel>
#include <QHBoxLayout>
#include <QDebug>
#include <QAbstractItemView>
#include <QModelIndex>
#include <QDataWidgetMapper>
#include <QShortcut>
#include <QKeySequence>
#include <QTextEdit>
#include <QHeaderView>

static bool createConnection()
{
    QSqlDatabase db = QSqlDatabase::addDatabase("QSQLITE");
    db.setDatabaseName(":memory:");
    if (!db.open()) {
        QMessageBox::critical(0, qApp->tr("Cannot open database"),
                              qApp->tr("Unable to establish a database connection.\n"
                                       "This example needs SQLite support. Please read "
                                       "the Qt SQL driver documentation for information how "
                                       "to build it.\n\n"
                                       "Click Cancel to exit."), QMessageBox::Cancel);
        return false;
    }

    QSqlQuery query;
    query.exec("create table person("
               "firstname varchar(1024), lastname varchar(1024))");
    query.exec("insert into person values('Danny', 'Young')");
    query.exec("insert into person values('Christine', 'Holand')");
    query.exec("insert into person values('Lars', 'Gordon')");
    query.exec("insert into person values('Roberto', 'Robitaille')");
    query.exec("insert into person values('Maria', 'Papadopoulos')");
    return true;
}

class MainWindow : public QMainWindow
{
    Q_OBJECT
public:
    MainWindow(QWidget *parent = 0)
        : QMainWindow(parent)
    {
        setCentralWidget(new QWidget(this));
        QVBoxLayout *lay = new QVBoxLayout(centralWidget());

        QHBoxLayout *hbox = new QHBoxLayout;

        QLabel *lbl = new QLabel("&firstName", centralWidget());
        hbox->addWidget(lbl);
        QLineEdit *firstName = new QLineEdit(centralWidget());
        hbox->addWidget(firstName);
        lbl->setBuddy(firstName);
        lay->addLayout(hbox);

        hbox = new QHBoxLayout;
        lbl = new QLabel("&lastName", centralWidget());
        hbox->addWidget(lbl);
        QLineEdit *lastName = new QLineEdit(centralWidget());
        hbox->addWidget(lastName);
        lbl->setBuddy(lastName);
        lay->addLayout(hbox);

        QSqlTableModel *model = new QSqlTableModel(this);
#if 1
        model->setEditStrategy(QSqlTableModel::OnFieldChange);
#else
        model->setEditStrategy(QSqlTableModel::OnManualSubmit);
#endif


        model->setTable("person");
        model->select();

        QTableView *view = new QTableView(centralWidget());
        view->setEditTriggers(QAbstractItemView::NoEditTriggers);
        view->setModel(model);
        view->horizontalHeader()->setStretchLastSection(true);
        connect(view->selectionModel(), SIGNAL(currentRowChanged(QModelIndex, QModelIndex)),
                this, SLOT(onSelected(QModelIndex)));
        lay->addWidget(view);

        mapper.setSubmitPolicy(QDataWidgetMapper::ManualSubmit);
        mapper.setModel(model);
        mapper.addMapping(firstName, 0);
        mapper.addMapping(lastName, 1);

        new QShortcut(QKeySequence(Qt::CTRL + Qt::Key_S), this, SLOT(save()));
        view->setSelectionBehavior(QAbstractItemView::SelectRows);
        view->setSelectionMode(QAbstractItemView::SingleSelection);
        view->selectRow(0);
    }
public slots:
    void save()
    {
        mapper.submit();
        qDebug() << "Submit failed";
    }
    void onSelected(const QModelIndex &index)
    {
        mapper.setCurrentModelIndex(index);
    }
private:
    QDataWidgetMapper mapper;
};

#include "main.moc"


int main(int argc, char **argv)
{
    QApplication a(argc, argv);
    if (!createConnection())
        return 1;

    MainWindow w;
    w.show();
    return a.exec();
}

bool QDataWidgetMapper::submit() 
{ 
    Q_D(QDataWidgetMapper); 
 
    for (int i = 0; i < d->widgetMap.count(); ++i) { 
        const QDataWidgetMapperPrivate::WidgetMapper &m = d->widgetMap.at(i); 
        if (m.widget.isNull()) 
            continue; 
        if (!m.currentIndex.isValid()) 
            return false; 
        d->delegate->setModelData(m.widget, d->model, m.currentIndex); 
    } 
 
    return d->model->submit(); 
} 

        if (!m.currentIndex.isValid())  <--
            return false;