public AppointmentEntity(List <TimeDuration> timeDurations
                          , CustomerEntity customer, List <Pet> pets, PaymentMethod paymentMethod)
 {
     Durations = timeDurations;
     Customer  = customer;
     Payment   = new Payment(Service.Price, new Price {
         Currency = Currency.UsDollars, Value = (Service.Price.Value * .25m)
     },
                             customer.Debit, paymentMethod);
     Customer.AddPayment(Payment);
     Pets = pets;
     AppointmentInstances = new List <AppointmentInstance>();
     foreach (var duration in Durations)
     {
         var instance = new AppointmentInstance {
             Date = duration.StartDateTime, AppointmentStatus = AppointmentStatus.Awaiting
         };
     }
 }