private void Btn_AddNewCustomer_Click_1(object sender, RoutedEventArgs e)
        {
            Customer c1 = new Customer();

            c1.FirstName          = tbx_AddFirstName.Text;
            c1.SecondName         = tbx_AddSecondName.Text;
            c1.Gender             = tbx_AddGender.Text;
            c1.Email              = tbx_AddEmail.Text;
            c1.PhoneNumber        = int.Parse(tbx_AddPhoneNumber.Text);
            c1.MembershipInMonths = int.Parse(tbx_AddMembership.Text);
            c1.StartDate          = DateTime.Now;
            c1.EmployeeId         = int.Parse(tbx_AddEmployeeId.Text);
            db.Customers.Add(c1);
            db.SaveChanges();
        }
        // Remove an employee from DB
        public static void RemoveEmoployeeByID(int selectedEmployee)
        {
            MessageBoxResult result = MessageBox.Show($"Are you sure you want to remove employee {selectedEmployee.ToString()}", "Are you sure?", MessageBoxButton.YesNo);

            switch (result)
            {
            case MessageBoxResult.Yes:
                using (var context = new GymContainer())
                {
                    try
                    {
                        var employee = context.Employees.Find(selectedEmployee);
                        context.Employees.Remove(employee);
                        context.SaveChanges();
                    }
                    catch (SystemException ex)
                    {
                        MessageBox.Show($"Exception: {ex}");
                    }
                }
                break;

            case MessageBoxResult.No:
                MessageBox.Show("Employee Not Removed");
                break;
            }
        }