Entity Framework AddTo object(s) with Foreign key

I have 2 table Reservation Guest

Reservation has a FK to Guest (GuestId)

When I add a new reservation I have to call AddTo on both objects for it to work. Which is fine, but I was thinking I should be able to set the guest object in the Reservation initializer and just call AddTo on the reservation object.

Is this the correct approach or am I missing something?

                var guest = new Guest
             开发者_JS百科   {
                    GuestId = Guid.NewGuid(),
                    LastName = item.Guest.LastName,
                    FirstName = item.Guest.FirstName
                };

                var reservation = new Reservation
                {
                    ReservationId = Guid.NewGuid(),
                    GuestId = guest.GuestId,
                    //Guest = guest,
                    ReservedDtm = item.Date
                };

                _context.AddToGuests(guest);
                _context.AddToReservations(reservation);

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Create the guest and use addObject(newguest) on the context. After that create the reservation and add the guest to it. That should work. I type from my smartphone so forgive me the missing formatation.