private void cbNumberTable_SelectionChanged(object sender, SelectionChangedEventArgs e)
 {
     Model.Table itemTable = (Model.Table)cbTable.SelectedItem;
     if (itemTable != null)
     {
         if (itemTable.IsBusy)
         {
             cbTable.SelectedItem = null;
             MessageBox.Show("Стол занят");
         }
     }
 }
        private void btnSaveZakaz_Click(object sender, RoutedEventArgs e)
        {
            double itogSum  = 0;
            bool   proverka = true;

            registrationZakaza.DateOpen = DateTime.Now;
            foreach (var item in db.ZakaznBludaNew)
            {
                if (item.IdZakaza == idNewZakaz)
                {
                    itogSum += (double)item.Price;
                }
            }
            registrationZakaza.Total = (int)itogSum;
            if (cbEmployee.SelectedItem != null)
            {
                registrationZakaza.EmployeeId = ((Employees)cbEmployee.SelectedItem).id;
            }
            else
            {
                MessageBox.Show("Поле Сотрудник не заполнено");
                proverka = false;
            }
            if (cbTable.SelectedItem != null)
            {
                registrationZakaza.NumberTable = ((Model.Table)cbTable.SelectedItem).Id;
                registrationZakaza.ZakazZakrit = false;
                Model.Table itemTable = db.Table.Where(i => i.NumberTable == ((Model.Table)cbTable.SelectedItem).NumberTable).FirstOrDefault();
                itemTable.IsBusy = true;
            }
            else
            {
                MessageBox.Show("Поле Стол не заполнено");
                proverka = false;
            }
            if (proverka != false)
            {
                db.RegistrationZakaza.Add(registrationZakaza);
                db.SaveChanges();
                idNewZakaz = registrationZakaza.Id;
                Close();
            }
        }