Rewrite it like this:
Qt Code: 
  1. MySQLConnect::MySQLConnect(QString db_user, QString db_pass, QString db_name, QString host, QString type) {
  2.   //connect to database
  3.   m_Database = QSqlDatabase::addDatabase(type);
  4.   m_Database.setHostName(host);
  5.   m_Database.setDatabaseName(db_name);
  6.   m_Database.setUserName(db_user);
  7.   m_Database.setPassword(db_pass);
  8.   bool openedOK =  m_Database.open();
  9.  
  10.   m_pModel = new QSqlRelationalTableModel(this);
  11.   Q_CHECK_PTR(m_pModel);
  12.   m_pModel->setEditStrategy(QSqlTableModel::OnManualSubmit);
  13. ...
  14. }
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replace m_pDatabase with m_Database (not a pointer).