Emit a signal only when an updated row is submitted to the database

Question

In my Qt 6.8.2 Desktop application I need to use the OnRowChange edit strategy for a QSqlRelationalTableModel, since it is a design constraint for the UX. To keep the UI consistent and synced with all the tables it is mandatory to know when a row is actually updated in the database.

In my previous question I found a way to emit a signal when the submit() slot is invoked. Here my own subclassing of the QSqlRelationalTableModel:

#include <QSqlRelationalTableModel>

class TableModel : public QSqlRelationalTableModel
{
    Q_OBJECT

public:
    explicit TableModel(QObject *parent = nullptr, const QSqlDatabase &db = QSqlDatabase()) : QSqlRelationalTableModel(parent, db)
    {
    }

public slots:
    bool submit() override
    {
        bool ret = QSqlRelationalTableModel::submit();
        if (ret) emit rowSubmitted();
        return ret;
    }

signals:
    void rowSubmitted();
};

This code solved the issue I had in the linked question, but going ahead with the development I noticed the submit() function is called every time the user changes a row, no matter if he has actually changed something in the model!

I cannot live with this limitation. So I tried to change this line to:

if (ret && isDirty()) emit rowSubmitted();

but in this case the signal is never emitted, even just after editing a row. I guess because the model was already updated at this time.

My goal is to emit the signal only when a row is actually submitted to the database. I searched in the docs a way to retrieve the rows (count) just submitted to the database but I found nothing.

How can I improve my code in order to emit the rowSubmitted() signal only when a row is really submitted to the database?

Answer 1

Here the correct implementation of the submit() function:

bool submit() override
{
    bool isDirtyShadow = isDirty();
    bool ret = QSqlRelationalTableModel::submit();
    if (ret && isDirtyShadow) emit rowSubmitted();
    return ret;
}

The trick is to save the isDirty() state before submitting to the database. Of course, after the changes are saved the model is not dirty anymore.