为什么@OneToMany 映射中存在循环？

Question

我正在尝试使用 JPA 创建一个@OneToMany 数据库。有一个对象 Flight 和一个对象 Passenger。

代码：

@Entity
@Table(name = "passengers")
public class Passenger {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private long id;
    
    @Column(name = "name")
    private String name;
    
    @Column(name = "surname")
    private String surname;
    
    private String email;
    
    private String phoneNumber;
    
    private String birthDate;
    
    @ManyToOne(optional = false)
    @JoinColumn(name = "flight_id")
    private Flight flight;
    
    public Passenger() {
    }
    
    public Passenger(String name, String surname, String email, String phoneNumber, String birthDate, Flight flight) {
        super();
        this.name = name;
        this.surname = surname;
        this.email = email;
        this.phoneNumber = phoneNumber;
        this.birthDate = birthDate;
        this.flight = flight;
    }

@Entity
@Table(name = "flights")
public class Flight {
    
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "flight_id")
    private long id;
    
    private String departure;
    
    private String destination;
    
    private String date;
    
    private int capacity;
    
    private float price;
    
    @OneToMany(fetch = FetchType.EAGER, mappedBy = "flight", cascade = CascadeType.ALL)
    private Set<Passenger> passengers;
    
    public Flight() {
        
    }

    public Flight(String departure, String destination, String date, int capacity, float price) {
        super();
        this.departure = departure;
        this.destination = destination;
        this.date = date;
        this.capacity = capacity;
        this.price = price;
    }

这是我添加新乘客的方式：

@PostMapping("/flights")
    public ResponseEntity<Object> updateFlight(@RequestBody Flight flight) {
        long id = flight.getId();
        Optional<Flight> flightOptional = flightRepository.findById(id);

        if (!flightOptional.isPresent())
            return ResponseEntity.notFound().build();

        int currentCapacity = flight.getCapacity();
        flight.setCapacity(currentCapacity - 1);

        for(Passenger passenger : flight.getPassengers()) {
            System.out.println(passenger.getName());
        } 

        this.flightRepository.save(flight);

        return ResponseEntity.noContent().build();
    }

不幸的是，当我绘制航班和乘客地图时，我似乎有一个永无止境的循环。乘客有航班和乘客的详细信息，然后是航班，然后是乘客，等等。

有什么办法可以解决吗？我错过了什么吗？

Answer 1

为了避免循环问题使用@JsonManagedReference, @JsonBackReference 如下。

在 Parent class

上添加 @JsonManagedReference

@JsonManagedReference
@OneToMany(fetch = FetchType.EAGER, mappedBy = "flight", c 
 ascadee = CascadeType.ALL)
private Set<Passenger> passengers;

在 child class 上添加 @JsonBackReference，如下所示

@JsonBackReference
@ManyToOne(optional = false)
@JoinColumn(name = "flight_id")
private Flight flight;

为什么@OneToMany 映射中存在循环？

Why is there a loop in @OneToMany mapping?

jpa

spring-data-jpa

mapping

one-to-many