How keep connection with MySQL Server 5

VladimirPivovar

During the execution of long-read data needed to communicate with the database server. Continuous check of connection to the server is required to insert a large number of records.

Please advise how to check the connection and how to deal with situations where one loses the connection to the database server

I can often cause the following code:

@
static QSqlDatabase db = QSqlDatabase::addDatabase("QMYSQL","Connection-To-MySQLServer-5.5");
static QSqlQuery query(db);

db.setHostName("localhost");
db.setPort(3306);
db.setUserName("root");
db.setPassword("root");
db.setDatabaseName("DataFromBinFiles");

if(!db.open())
{
    MessageBox (hwnd, "---",
    "Lost Connection", MB_OK|MB_ICONINFORMATION);
    return FALSE;
}
 else
{
    MessageBox (hwnd, "---",
    "Success", MB_OK|MB_ICONINFORMATION);
    return TRUE;
}

@

ChrisW67

Your code has nothing to do with losing a connection. It's only creating a connection and either succeeding or failing.

If an existing connection is lost between your machine and the server then queries will start failing. The QSqlQuery::lastError() call should return an error of type QSqlError::ConnectionError. You can also periodically check QSqlDatabase::isOpen(). Since you are using MySQL you can also use the MYSQL_OPT_RECONNECT in QSqlDatabase::setConnectOptions() to automatically attempt reconnection (it might still fail).

How you recover, if possible at all, is dependent on your application. If you have been working inside a transaction the server has probably already rolled back the transaction so you need to recover at that point in your application's processing.