QSqlDatabase::removeDatabase problem

[xeroblast]

this is my code :

mydb.cpp

#include <QSqlDatabase>
QSqlDatabase MyDB::connectDatabase()
{
  QSqlDatabase db = QSqlDatabase::addDatabase("QMYSQL");
  // below are usernames & passwords & ports & etc...
  return db;
}
 
void MyDB::removeConnection()
{
  QSqlDatabase::removeDatabase("QMYSQL");
}

#include <QSqlDatabase>
QSqlDatabase MyDB::connectDatabase()
{
  QSqlDatabase db = QSqlDatabase::addDatabase("QMYSQL");
  // below are usernames & passwords & ports & etc...
  return db;
}

void MyDB::removeConnection()
{
  QSqlDatabase::removeDatabase("QMYSQL");
}

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mainwindow.cpp

#include "mydb.h"
MyDB mydb;
MainWindow::MainWindow()
{
  {
    QSqlDatabase db = mydb.connectDatabase();
    QSqlQuery query;
    // perform queries here
    query.clear();
    db.close();
  }
  mydb.removeDatabase(); // not working here
}

#include "mydb.h"
MyDB mydb;
MainWindow::MainWindow()
{
  {
    QSqlDatabase db = mydb.connectDatabase();
    QSqlQuery query;
    // perform queries here
    query.clear();
    db.close();
  }
  mydb.removeDatabase(); // not working here
}

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i still get this error : QSqlDatabasePrivate::addDatabase: duplicate connection name 'qt_sql_default_connection', old connection removed.
what am i missing? i already read the docs about QSqlDatabase::removeDatabase()...
thanks...