from PySide6.QtWidgets import QApplication, QMainWindow
from PySide6 import QtSql
from pyqt5_gui import Ui_MainWindow

class Frm_main(QMainWindow, Ui_MainWindow):
    def __init__(self):
        super().__init__()
        self.setupUi(self)
        mod_geraete = QtSql.QSqlRelationalTableModel()
        mod_geraete.setTable("Geraete")
        mod_geraete.setRelation(2, QtSql.QSqlRelation("Kunden", "Kunden_Index", "Kunden_Name"))
        mod_geraete.setRelation(6, QtSql.QSqlRelation("Pruefung", "Pruefung_Ablauf", "Pruefung_Name"))
        mod_geraete.select()
        self.tbl_geraete.setModel(mod_geraete)

db = QtSql.QSqlDatabase.addDatabase("QSQLITE")
db.setDatabaseName("meine.db")


app = QApplication()
frm_main = Frm_main()
frm_main.lbl_eins.setText("Ein Label")
#self.lbl_eins.setText(QCoreApplication.translate("MainWindow", u"Das Label", None))
frm_main.show()
app.exec()