Qsqlite duplicate connection warning in qt c++

Question

I am creating an application in qt which uses sqlite database. I have written a class to open database connection. The constructor for the class is given below:

currencydb::currencydb()
{

    currency = QSqlDatabase::addDatabase("QSQLITE");
    currency.setDatabaseName("currency.sqlite");
    if(!currency.isOpen())
    {

        if (!currency.open())
        {
            qDebug() << "Error: connection with database fail";
        }
        else
        {
            qDebug() << "Database currency: connection ok";
        }
    }
}

Since i use this constructor, when i create object for the database class, i get following warning:

QSqlDatabasePrivate::addDatabase: duplicate connection name 'qt_sql_default_connection', old connection removed.

Is there a way to check whether the database is already open?

talamaki · Accepted Answer · 2016-05-04 17:49:39Z

That warning doesn't mean that your database is already open but that you already have a connection to the database with a default name. The connection provides access to the database via (in your case SQLITE v3) database driver. You create a default connection to the database when you don't pass the connection name argument when you call static public method QSqlDatabase::addDatabase().

You can use QSqlDatabase::contains() for checking if you already have the default connection.

CurrencyDb::CurrencyDb()
{
    currency = openDb("QSQLITE", "currency.sqlite");
}

QSqlDatabase CurrencyDb::openDb(const QString &driver, const QString &name) const
{
    QSqlDatabase db;

    // contains() default argument is initialized to default connection
    if (QSqlDatabase::contains())
    {
        db = QSqlDatabase::database(QLatin1String(QSqlDatabase::defaultConnection), false);
    }
    else
    {
        db = QSqlDatabase::addDatabase(driver.toUpper());
    }

    db.setDatabaseName(name);

    if (!db.isValid())
    {
        // Log error (last error: db.lastError().text()) and throw exception
    }

    if (!db.open())
    {
        // Log error (last error: db.lastError().text()) and throw exception
    }

    return db;
}

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