connection 'qt_sql_default_connection' is still in use, all queries will cease to work.

[rahulvishwakarma]

hi to all, I've qt 5.7 in centos7. I am facing problem of connection "'qt_sql_default_connection' is still in use, all queries will cease to work." When i start program it errors like :

QSqlDatabasePrivate::removeDatabase: connection 'qt_sql_default_connection' is still in use, all queries will cease to work. QSqlDatabasePrivate::addDatabase: duplicate connection name 'qt_sql_default_connection', old connection removed.

mine starting code is :-

#include "dialoglogin.h"
#include "ui_dialoglogin.h"

DialogLogin::DialogLogin(QWidget *parent) :
    QDialog(parent),
    ui(new Ui::DialogLogin)
{
    ui->setupUi(this);
    //QString database = "cbsdb";
    db = new QSqlDatabase(QSqlDatabase::addDatabase("QMYSQL"));//, "cbsdb"));
    db->setDatabaseName("cbs");
    db->setHostName("serverora.db.net");
    db->setUserName("rahul");
    db->setPassword("rahul");
    db->setPort(3306);
    db->setConnectOptions();
    dlgmenu = new DialogMenu(this);
    query = new QSqlQuery;
}

DialogLogin::~DialogLogin()
{
    QSqlDatabase::database().close();
    delete db;
    delete ui;
}

void DialogLogin::on_pushButtonCancel_clicked()
{

    exit(0);
}

void DialogLogin::on_pushButtonLogin_clicked()
{
    if(db->open())
    {
        QMessageBox::information(this, "inside DialogLogin::db->open ","inside db->open");
        sql = "select User from tableLogin where User = ? and Password = ?";

        QString user = ui->lineEditUserName->text().trimmed();
        QString password = ui->lineEditPassword->text().trimmed();
        if(!query->prepare(sql))
        {
            QMessageBox::information(this, "inside DialogLogin::query->prepare", "Error : " + query->lastError().text());
            return;
        }

        query->bindValue(0, user);
        query->bindValue(1, password);

        if(query->exec())
        {
            if(query->next())
            {
                if(QString::compare(user, query->value(0).toString().trimmed()) == 0) // && ( QString::compare(password, query->value(1).toString().trimmed()) == 0) )
                {
                    this->close();
                    dlgmenu->exec();                    
                }
                else
                {
                    QMessageBox::information(this, "Login Form", "user name or password is incorrect");
                }
            }
            else
            {
                QMessageBox::information(this, "Login Form", "query.next() is failed : " + query->lastError().text());
            }
        }
        else
        {
            QMessageBox::information(this, "Login Form", " Error in login " + query->lastError().text());
        }
    }
    else
    {
        QMessageBox::information(this,"cbs LoginForm", "database cannot be openned : " + db->lastError().text());
    }
}

error is :-

[jsulm]

@rahulvishwakarma said in connection 'qt_sql_default_connection' is still in use, all queries will cease to work.:

db = new QSqlDatabase(QSqlDatabase::addDatabase("QMYSQL"));//, "cbsdb"));

Why do you have this db variable? Please check documentation to see how to properly use https://doc.qt.io/qt-5/qsqldatabase.html
Also, it does not make sense to create a new connection and then second one and use the first one as parameter! You're calling copy constructor this way...

[rahulvishwakarma]

because db is pointer so i have to do this
db = new QSqlDatabase(QSqlDatabase::addDatabase("QMYSQL"));

after that i use this to connect database with front end.

[jsulm]

@rahulvishwakarma said in connection 'qt_sql_default_connection' is still in use, all queries will cease to work.:

so i have to do this

No, you don't!
Please read documentation!
There is no need to create a QSqlDatabase instance manually - that is what addDatabase() does for you...

[rahulvishwakarma]

can you please tell me by example how to do it. Actually i have another mini project that accepts this.

[jsulm]

@rahulvishwakarma There is an example in the documentation I pointed you to

[JonB]

@rahulvishwakarma
As @jsulm pointed you to, the very first example at https://doc.qt.io/qt-5/qsqldatabase.html#details shows you what you are supposed to do.