public EmployeeDto getEmployeeById(int employeeId)
        {
            EmployeeDto employee = new EmployeeDto();

            if (employeeId > 0)
            {
                using (var _context = new NorthwindEntities())
                {
                    Employee empl = _context.Employees.First(x => x.EmployeeID == employeeId);

                    employee = new EmployeeDto()
                    {
                        EmployeeId = empl.EmployeeID,
                        Vorname = empl.FirstName,
                        Nachname = empl.LastName,
                        Adresse = empl.Address,
                        Stadt = empl.City,
                        PLZ = empl.PostalCode,
                        Land = empl.Country,
                        Geburtsdatum = empl.BirthDate,
                        Einstellungsdatum = empl.HireDate,
                        Telefon = empl.HomePhone
                    };
                }
            }
            return employee;
        }
        private void Window_Loaded(object sender, RoutedEventArgs e)
        {
            using (NorthwindEntities _context = new NorthwindEntities())
            {
                Employee empl = _context.Employees.First(x => x.EmployeeID == this.EmployeeId);

                _employee = new EmployeeDto()
                {
                    EmployeeId = empl.EmployeeID,
                    Vorname = empl.FirstName,
                    Nachname = empl.LastName,
                    Adresse = empl.Address,
                    Stadt = empl.City,
                    PLZ = empl.PostalCode,
                    Land = empl.Country,
                    Geburtsdatum = empl.BirthDate,
                    Einstellungsdatum = empl.HireDate,
                    Telefon = empl.HomePhone
                };

                this.DataContext = _employee;
            }
        }
        private void HandleEmployeeDto(EmployeeDto employee)
        {
            var e = _context.Employees.First(x => x.EmployeeID == employee.EmployeeId);
            e.FirstName = employee.Vorname;
            e.LastName = employee.Nachname;
            e.Country = employee.Land;
            e.Address = employee.Adresse;
            e.City = employee.Stadt;
            e.HomePhone = employee.Telefon;
            e.PostalCode = employee.PLZ;

            _context.SaveChanges();
            this.Dispatcher.Invoke((Action)(() => employeeDataGrid.Items.Refresh()));
        }