public IHttpActionResult CreateAppointment(AppointmentModel model) { if (!ModelState.IsValid) { return(BadRequest(ModelState)); } // Check if the patient already have one appointment for the given date Domain.Appointment appointment = _appointmentHelper.GetAppointmentsByPatient(model.PatientId).Where(a => a.AppointmentDateTime.Date == model.AppointmentDateTime.Date).FirstOrDefault(); // No appointments for the given date if (appointment == null) { _appointmentHelper.CreateAppointment(model); return(Ok("Success")); } else { return(Ok(string.Format("You already have an appointment for {0}", model.AppointmentDateTime.ToString("yyyy-MM-dd")))); } }