Java spring boot中用于持久化数据的多对多关系的JPA或CRUD存储库查询

我有3个实体城市、酒店和书房，地图如下所述：

public class BookRoom {

  @Id
  @GeneratedValue(strategy = GenerationType.AUTO)
  private int bookID;
  .....
  .....
  @ManyToOne(fetch = FetchType.LAZY, cascade = CascadeType.ALL)
  @JoinColumn(name ="hotelID")
  private Hotel hotel;
}  

public class Hotel {

  @Id
  @GeneratedValue(strategy = GenerationType.AUTO)
  private Integer hotelID;
  ....
  ....
  @ManyToMany(fetch = FetchType.LAZY, cascade = CascadeType.ALL)
  @JoinTable(name = "Hotel_City", joinColumns = @JoinColumn(name = "hotelID", nullable = false), inverseJoinColumns = @JoinColumn(name = "cityID", nullable = false))
  private Set<City> cities;

  @OneToMany(fetch = FetchType.LAZY, mappedBy = "hotel")
  private Set<BookRoom> bookRoom;
}

public class City {

  @Id
  @GeneratedValue(strategy = GenerationType.AUTO)
  private int cityID;
  ....
  ....
  @ManyToMany(fetch = FetchType.LAZY, mappedBy = "cities")
  private Set<Hotel> hotels;
}

我的调用方法如下：

@Override
public void run(String... arg0) throws Exception {
    City city = new City();
    Hotel hotel = new Hotel();
    city.setCityID(4);
    Set<City> cities = new HashSet<>();
    cities.add(city);
    hotel.setCities(cities );
    hotel.setHotelID(2);

    BookRoom bookRoom = new BookRoom();
    bookRoom.setCheckInDate(new Date());
    bookRoom.setCheckOutDate(new Date());
    bookRoom.setCityN("Ranchi");
    bookRoom.setNoOfRooms(1);
    bookRoom.setHotel(hotel);
    bookRoom.setUserName("Aman");
    bookRoomRepo.save(bookRoom);
}

@覆盖
公共无效运行（字符串…arg0）引发异常{
城市=新城（）；
酒店=新酒店（）；
城市。设置城市ID（4）；
Set cities=newhashset（）；
城市。添加（城市）；
塞特城市酒店（城市）；
塞特霍特利德酒店（2）；
书房书房=新书房（）；
bookRoom.setCheckInDate（新日期（））；
bookRoom.setCheckOutDate（新日期（））；
书房：setCityN（“Ranchi”）；
书房.书房（1）；
书房。塞特酒店（酒店）；
bookRoom.setUserName（“Aman”）；
bookRoomRepo.save（bookRoom）；
}

因此，我的问题是，在添加BookRoom详细信息时，它会尝试添加酒店和城市的记录，而不管数据是否存在。

尝试使用merge（）方法，而不是save（）方法。请参见

可能的副本

Caused by: org.hibernate.PersistentObjectException: detached entity passed to persist: com.hbs.entity.Hotel

@Override
public void run(String... arg0) throws Exception {
    City city = new City();
    Hotel hotel = new Hotel();
    city.setCityID(4);
    Set<City> cities = new HashSet<>();
    cities.add(city);
    hotel.setCities(cities );
    hotel.setHotelID(2);

    BookRoom bookRoom = new BookRoom();
    bookRoom.setCheckInDate(new Date());
    bookRoom.setCheckOutDate(new Date());
    bookRoom.setCityN("Ranchi");
    bookRoom.setNoOfRooms(1);
    bookRoom.setHotel(hotel);
    bookRoom.setUserName("Aman");
    bookRoomRepo.save(bookRoom);
}