I am quite new to Spring boot in general and I am trying to create an REST API application. I have ran into this problem. When I try to post an entity that references another via the foreign key I get this error message:

 "messsage": "org.hibernate.TransientPropertyValueException: 
object references an unsaved transient instance - save the transient instance before flushing : 
com.internationalairport.airportmanagementsystem.entities.BoardingPass.ticket -> 
com.internationalairport.airportmanagementsystem.entities.Ticket"

I have two entities that share a one to one relation ship. Here’s is the first entity SQL table tickets structure:

CREATE TABLE IF NOT EXISTS tickets (
    ticket_id INT AUTO_INCREMENT PRIMARY KEY,
    flight_id INT,
    passenger_id INT,
    seat_number VARCHAR(6),
    class VARCHAR(15),
    price DECIMAL(10, 2),
    FOREIGN KEY (flight_id) REFERENCES flights(flight_id),
    FOREIGN KEY (passenger_id) REFERENCES passengers(passenger_id)
);

Here is the structure for the other table boarding_passes that references the flights table:

CREATE TABLE IF NOT EXISTS boarding_passes (
    boarding_pass_id INT AUTO_INCREMENT PRIMARY KEY,
    ticket_id INT,
    gate VARCHAR(10),
    boarding_time DATETIME NOT NULL,
    FOREIGN KEY (ticket_id) REFERENCES tickets(ticket_id)
);

Here is the ticket JPA entity (some methods and fields have not been added for brevity sake.

@Entity
@Table(name = "tickets")
public class Ticket {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "ticket_id")
    private Integer ticketId;
  
    //Other fields and methods not added for brevity
   
    @OneToOne(mappedBy = "ticket", cascade = CascadeType.ALL)
    @JsonManagedReference
    private BoardingPass boardingPass;

Here is the Boarding Pass entity:

@Entity
@Table(name = "boarding_passes")
public class BoardingPass {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "boarding_pass_id")
    private Integer boardingPassId;

    //Other fields and methods not added for brevity

    @OneToOne
    @JoinColumn(name = "ticket_id")
    @JsonBackReference
    private Ticket ticket;

Now I am going to explain the process that my application follows to post a Boarding Pass record. I am making use of DTOs. So I send an HTTP POST request via postman that has this body content: (The ticked has been previously created I don’t need to create it again)

{
    "ticketId" : 1,
    "gate" : "3B",
    "boardingTime" : "2024-01-01T12:52:11"
}

I handle the POST Request in this endpoint:

@PostMapping("/boarding_passes")
    public BoardingPass addBoardingPass(@RequestBody PostBoardingPassDto postBoardingPassDto){
        return boardingPassService.save(postBoardingPassDto);
    }

Here is the post Boarding Pass Dto:

public record PostBoardingPassDto(
    Integer tickedId,
    String gate,
    LocalDateTime boardingTime
) {
}

Here is the service method that is supposed to save this entity using the default JPARepository method save():

@Override
    public BoardingPass save(PostBoardingPassDto postBoardingPassDto) {
        BoardingPass boardingPass = boardingPassMapper.toBoardingPass(postBoardingPassDto);
        return boardingPassRepository.save(boardingPass);
    }

The boardingPassMapper transforms a DTO to an Entity it is implemented like this:

@Service
public class BoardingPassMapper {
    public BoardingPass toBoardingPass(PostBoardingPassDto postBoardingPass){
        BoardingPass boardingPass = new BoardingPass(
                postBoardingPass.gate(),
                postBoardingPass.boardingTime()

        );
        Ticket ticket = new Ticket();
        ticket.setTicketId(postBoardingPass.tickedId());

        boardingPass.setTicket(ticket);
        return boardingPass;
    }
}

So I have used the same approach in @ManyToOne entities but I haven’t had any problems. However, here I am missing something. So I’m trying to insert a boarding pass which has a foreign key of an already existing Ticket. So then that ticket will have a boarding pass object in it. I don’t need to create a new ticket when I make a POST request(hence why I don’t have a Cascade.ALL type in the Boarding Pass entity. Here is a full screenshot:

So if anybody could help me out I would really appreciate it. I’ve been stuck for a long time. Any form of suggestion helps.