MySQL doesn't return data

[Izba]

Hi i'm having problems with reading data out of database.

The connection should be fine as bool ok = m_db.open() returns 1.

i connect to database like this:

    m_db = QSqlDatabase::addDatabase("QMYSQL");
    m_db.setHostName(m_hostname);
    m_db.setUserName(m_username);
    m_db.setPort(m_port);
    m_db.setPassword(m_password);
    bool ok = m_db.open();

Then i select dbname with other function:

void SqlDB::SelectDB(QString &dbname){
    std::cout <<"SelectDB" << " " << dbname.toStdString() << std::endl;
    m_db.setDatabaseName(dbname);
}

And then i try to use other function to get the data.

    std::cout <<"GetTables" << std::endl;
    QSqlDriver *driver = m_db.driver();
    std::cout << "isopen:" << m_db.isOpen();
    std::cout << "db name=" <<m_db.databaseName().toStdString();
    QSqlRecord record = driver->record("auto");
    QSqlQuery q;
    q.exec("SELECT * from auto");
    while(q.next()){
        QString val;
        val = q.value(0).toString();
        std::cout << val.toStdString();
    }
    std::cout << "record count = " << record.count();

isopen = 1,
dbname is correct, but it still gives me record.count() = 0.

I have also tried to use db.tables(), but it returns 0 lines too.

Thanks,
Izba

[jsulm]

@Izba What does http://doc.qt.io/qt-5/qsqlquery.html#lastError return?

[Izba]

@jsulm

    QSqlError err = m_db.lastError();
    std::cout << err.databaseText().toStdString();
    std::cout << err.text().toStdString();
    std::cout << err.driverText().toStdString();

I cant get it to return anything. Maybe i'm trying to debug it wrong?

[jsulm]

@Izba I mean the error from QSqlQuery

QSqlQuery q;
q.exec("SELECT * from auto");
while(q.next()){
    QString val;
    val = q.value(0).toString();
    std::cout << val.toStdString();
}
std::cout << "record count = " << record.count();
qDebug() << q.lastError();

[Izba]

@jsulm said in MySQL doesn't return data:

val = q.value(0).toString();
std::cout << val.toStdString();

}
std::cout << "record count = " << record.count();
qDebug() << q.lastError();

Oh yeah it gives me an error that no database selected, but m_db.databaseName still gives me correct database.

I have set the database by m_db.setDatabaseName().

Do i need to set it some other way that the query would recognize it?

Thanks

[jsulm]

@Izba Try to pass the db as parameter:

QSqlQuery q(QSqlDatabase::database("YOURDBNAME"));

[Izba]

@jsulm

  QSqlQuery q(QSqlDatabase::database("mottonen"));
    q.exec("SELECT * from auto");
    while(q.next()){
        QString val;
        val = q.value(0).toString();
        std::cout << val.toStdString();
    }
    qDebug() << q.lastError();

Still same error:

QSqlError("1046", "QMYSQL: Kyselyn suorittaminen epäonnistui", "No database selected")

[jsulm]

@Izba

QSqlQuery q(m_db);

[Izba]

@jsulm

No change at all. Still the same error that database is not selected.

[jsulm]

@Izba Please read documentation:
"Sets the connection's database name to name. To have effect, the database name must be set before the connection is opened."
http://doc.qt.io/qt-5/qsqldatabase.html#setDatabaseName

[Izba]

@jsulm
Yeah thank you a lot that did it! Guess i have skipped that part.

thanks,
izba