private void AddTrip(Trip trip, ITripService tripService, IAreaService areaService, IUserService userService) { trip.User = userService.FindByEmail(trip.User.Email); if (trip.User == default(User)) { throw new Exception("User doesn't exists."); } trip.Area = areaService.FindById(trip.Area.Id); if (trip.Area == default(Area)) { throw new Exception("Area doesn't exists."); } tripService.Add(trip); }