Find what is using a `QSqlDatabase` connection

[Mark81]

Here my code:

Orders::Orders(QObject *parent) : QObject{parent}
{
        QSqlDatabase db = QSqlDatabase::addDatabase("QMYSQL", "orders");
        db.setHostName("localhost");
        db.setDatabaseName("database");
        db.setUserName("user");
        db.setPassword("password");
        db.setConnectOptions("MYSQL_OPT_RECONNECT=TRUE;");
        _isConnected = db.open();
    
        if (_isConnected)
        {
            _model = new QSqlTableModel(this, db);
            _model->setTable("orders");
            _model->setEditStrategy(QSqlTableModel::OnManualSubmit);
            _model->select();
        }
    }

Orders::~Orders()
{
    if (_model) _model->clear();
    QSqlDatabase db = QSqlDatabase::database("orders");
    db.close();
    QSqlDatabase::removeDatabase("orders");
}

I don't have any QSqlDatabase nor QSqlQuery class member. I always create them inside the functions, example:

void Orders::setOrderState(QString machine, QString id, DbOrderStates state)
{
    QSqlDatabase db = QSqlDatabase::database("orders");
    QString sql = QString("UPDATE orders SET states_id=:state WHERE id=:id AND machine=:machine");

    QSqlQuery query(db);
    query.prepare(sql);
    query.bindValue(":state", static_cast<int>(state));
    query.bindValue(":id", id);
    query.bindValue(":machine", machine);
    query.exec();
}

Still, it complains when I close the application:

QSqlDatabasePrivate::removeDatabase: connection 'orders' is still in use, all queries will cease to work.

I can't understand what is still in use... is there a way to find out what is using the connection?

[JonB]

@Mark81
If you try a standalone program with just Orders::Orders() & Orders::~Orders() in it do you still get the message? My first thought is that you do have a QSqlQuery or similar left lying around somewhere.

Hang on! I think it is your Orders::~Orders() which is the issue. You cannot QSqlDatabase::removeDatabase("orders") in the same scope as QSqlDatabase db = QSqlDatabase::database("orders");. You need:

    {
        QSqlDatabase db = QSqlDatabase::database("orders");
        db.close();
    }
    QSqlDatabase::removeDatabase("orders");

This is even shown in https://doc.qt.io/qt-6/qsqldatabase.html#removeDatabase.

[Mark81]

@JonB I read that paragraph dozen of times but I didn't realize the braces are intended to be literal! I understood it's just to point out I need to place the variables inside a function!

Anyway it still wasn't enough!
I had to add:

delete _model;

even if the docs says:

Clears the model and releases any acquired resource.