QT6 Can't read the OUT parameter from MYSQL Database

roditu

Hi I have MYSQL Database on Azure, I made a simple Procedure with OUT Parameter and c++ method exactly as documentation instructed me:
https://doc.qt.io/qt-5/qsqlquery.html#approaches-to-binding-values

CREATE PROCEDURE validate_credentials(IN in_login VARCHAR(20), IN in_password VARCHAR(20), INOUT out_is_valid BOOLEAN)
BEGIN
    SET out_is_valid = TRUE;
    SELECT TRUE INTO out_is_valid;
END;

All it does is set the out_is_valid to TRUE, and it doesn't matter if it's OUT or INOUT in c++ or mysql it won't work regardless.

{
    QSqlQuery query{};

    bool isValid{false};

    //validate_credentials(IN in_login VARCHAR(20), IN in_password VARCHAR(20), OUT out_is_valid BOOLEAN)
    query.prepare("CALL validate_credentials(?, ?, ?)");

    query.bindValue(0, login);
    query.bindValue(1, password);
    query.bindValue(2, QVariant(false), QSql::InOut);

    if(query.exec()){
        isValid = query.boundValue(2).toBool();
        qInfo() << isValid;
    }

    else{
        qWarning() << "Failed to execute validate_credentials: " << query.lastError().text();
    }

    return isValid;
}

The problem is that it doesn't change the binded OUT parameter, so if it's value like in here it stays as false after reading (in qInfo() << isValid it prints false instead of true).

I truly don't understand why this is wrong, is QT like bugged lol?

Christian Ehrlicher

I had some time and found the reason: https://doc.qt.io/qt-6/sql-driver.html#qmysql-for-mysql-or-mariadb-5-6-and-higher

q.prepare("CALL validate_credentials(?, ?, @outval1)");
q.bindValue(0, "login");
q.bindValue(1, "password");
if (!q.exec()) {
    qDebug() << q.lastError();
    return 1;
}
if (q.exec("select @outval1")) {
    if (q.next()) {
        bool isValid = q.value(0).toBool();
        qInfo() << isValid;
    }
} else {
    qWarning() << "Failed to execute validate_credentials: " << q.lastError().text();
}

Christian Ehrlicher

Can you please fill a bug report with a minimal, compilable example? I can't find a good explanation why it does not work (or even how it was supposed to work) and need some time to investigate. Please also post a link to the bug report here.

roditu

@Christian-Ehrlicher https://bugreports.qt.io/browse/QTBUG-118552

roditu

@Christian-Ehrlicher added compilable example

Christian Ehrlicher

I had some time and found the reason: https://doc.qt.io/qt-6/sql-driver.html#qmysql-for-mysql-or-mariadb-5-6-and-higher

q.prepare("CALL validate_credentials(?, ?, @outval1)");
q.bindValue(0, "login");
q.bindValue(1, "password");
if (!q.exec()) {
    qDebug() << q.lastError();
    return 1;
}
if (q.exec("select @outval1")) {
    if (q.next()) {
        bool isValid = q.value(0).toBool();
        qInfo() << isValid;
    }
} else {
    qWarning() << "Failed to execute validate_credentials: " << q.lastError().text();
}

roditu

@Christian-Ehrlicher thank You very much