I have got this far (with check connection first only):

mysql.h:
Qt Code: 
  1. #ifndef MYSQL_H
  2. #define MYSQL_H
  3.  
  4. #include <QObject>
  5.  
  6. class MySQL : public QObject
  7. {
  8.     Q_OBJECT
  9. public:
  10.     explicit MySQL(QObject *parent = 0);
  11.     Q_INVOKABLE void checkConnection();
  12.  
  13. signals:
  14.  
  15. public slots:
  16.  
  17. };
  18.  
  19. #endif // MYSQL_H
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mysql.cpp:
Qt Code: 
  1. #include "mysql.h"
  2. #include <QtSql>
  3. #include <QObject>
  4.  
  5. MySQL::MySQL(QObject *parent) :
  6.     QObject(parent)
  7. {
  8. }
  9.  
  10. void MySQL::checkConnection()
  11. {
  12.     QString result;
  13.     // Sets database
  14.     QSqlDatabase db = QSqlDatabase::addDatabase("QMYSQL");
  15.     db.setHostName("localhost");
  16.     db.setDatabaseName("terminals");
  17.     db.setUserName("root");
  18.     db.setPassword("");
  19.  
  20.     if(db.open()) { qDebug() << "MySQL: Connected"; db.close(); result = "true"; }
  21.     else { qDebug() << "MySQL ERROR: " << db.lastError().text(); result = "false"; }
  22.  
  23. }
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main.qml:
Qt Code: 
  1. import QtQuick 2.12
  2. import QtQuick.Controls 2.0
  3. import QtQuick.LocalStorage 2.0
  4. import MySQL 1.0
  5. import 'JavaScript.js' as JS
  6.  
  7. Item {
  8.  
  9.     MySQL {
  10.         id: sql
  11.     }
  12.  
  13.     MouseArea {
  14.         anchors.fill: parent
  15.         onClicked: { sql.checkConnection(); }
  16.     }
  17. }
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main.cpp:
Qt Code: 
  1. #include <QtCore>
  2. #include <QNetworkAccessManager>
  3. #include <QNetworkReply>
  4. #include <QGuiApplication>
  5. #include <QQmlApplicationEngine>
  6. #include <QtSql>
  7. #include <QtDebug>
  8. #include "mysql.h"
  9.  
  10. int main(int argc, char *argv[])
  11. {
  12.     QGuiApplication app(argc, argv);
  13.  
  14.     qmlRegisterType<MySQL>("MySQL", 1, 0, "MySQL");
  15.  
  16.     QQmlApplicationEngine engine;
  17.     engine.load(QUrl(QStringLiteral("qrc:/main.qml")));
  18.  
  19.     // Sets path for SQLite
  20.     engine.setOfflineStoragePath("C:\\Terminal");
  21.  
  22.     return app.exec();
  23. }
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¨

this works like a charm!

i would like to ad the return ability, so from QML i can do something like:
if(sql.checkConnection()===true) { something } else { somethingelse }
- so it will return result variable from mysql.cpp

how to do this?