QSqlDatabasePrivate::addDatabase: duplicate connection name 'MyConnection' error

[Lasith]

I have written a Qt program in c++ inorder to access a database and load database tables to table view! My program does not show any compile errors but gives 2 runtime errors

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

There are mainly to classes namely MainWindow(Has database connection methods) and Dialog Following are my codes

MainWindow.h

class MainWindow : public QMainWindow
{
    Q_OBJECT

public:
    explicit MainWindow(QWidget *parent = 0);
    ~MainWindow();

public: QSqlDatabase mydb;
        bool conOpen(QString userName,QString password,QString hostname,int port,QString service){
            mydb=QSqlDatabase::addDatabase("QOCI","MyConnection");
            mydb.setUserName(userName);
            mydb.setPassword(password);
            mydb.setHostName(hostname);
            mydb.setPort(port);
            mydb.setDatabaseName(service);
            return mydb.open();

}

MainWindow.cpp

void MainWindow::on_pushButton_clicked()
{
    Dialog *dialog1 = new Dialog(this);
   if(conOpen(ui->uname->text(),ui->pword->text(),ui->ip->text(),ui->port->text().toInt(),ui->service->text())){

        dialog1->show();
}

Dialog.h

class Dialog : public QDialog
{
    Q_OBJECT

public:
    explicit Dialog(QWidget *parent = 0);
    ~Dialog();

private slots:
    void on_pushButton_clicked();

Dialog.cpp

void Dialog::on_pushButton_clicked()
{

    QSqlQueryModel *modal = new QSqlQueryModel();
    if(QSqlDatabase::contains("MyConnection")){

        QSqlQuery* qry=new QSqlQuery(QSqlDatabase::database("MyConnection"));
        qry->prepare("select NAME FROM Employees");
           qry->exec();
        modal->setQuery(*qry);
      ui->tableView->setModel(modal);

    }
}

The MainWindow form is used for login and Dialog form is used to retrieve entries in database table to a table view How can I correct the issue?

Please take care to use the code tags where appropriate when making a post ~kshegunov

[Added code tags ~kshegunov]

[jsulm]

@Lasith You should open the database only once. Currently you do it each time button is pressed.