我想獲取旅館資料但顯示錯誤。有人有解決方案嗎？

我正在使用 Spring Boot 應用程式使用 JPA 存盤庫創建稱為宿舍管理系統的應用程式。我增加了一間旅館。然后我添加了房間，然后更新旅館以更新連接表條目。現在我正在嘗試取宿舍。無法獲取宿舍資料，它顯示：

at com.fasterxml.jackson.databind.ser.BeanSerializer.serialize(BeanSerializer.java:178) ~[jackson-databind-2.13.4.2.jar:2.13.4.2]
    at com.fasterxml.jackson.databind.ser.BeanPropertyWriter.serializeAsField(BeanPropertyWriter.java:728) ~[jackson-databind-2.13.4.2.jar:2.13.4.2]
    at com.fasterxml.jackson.databind.ser.std.BeanSerializerBase.serializeFields(BeanSerializerBase.java:774) ~[jackson-databind-2.13.4.2.jar:2.13.4.2]
    at com.fasterxml.jackson.databind.ser.BeanSerializer.serialize(BeanSerializer.java:178) ~[jackson-databind-2.13.4.2.jar:2.13.4.2]
    at com.fasterxml.jackson.databind.ser.std.CollectionSerializer.serializeContents(CollectionSerializer.java:145) ~[jackson-databind-2.13.4.2.jar:2.13.4.2]
    at com.fasterxml.jackson.databind.ser.std.CollectionSerializer.serialize(CollectionSerializer.java:107) ~[jackson-databind-2.13.4.2.jar:2.13.4.2]
    at com.fasterxml.jackson.databind.ser.std.CollectionSerializer.serialize(CollectionSerializer.java:25) ~[jackson-databind-2.13.4.2.jar:2.13.4.2]
    at com.fasterxml.jackson.databind.ser.BeanPropertyWriter.serializeAsField(BeanPropertyWriter.java:728) ~[jackson-databind-2.13.4.2.jar:2.13.4.2]
    at com.fasterxml.jackson.databind.ser.std.BeanSerializerBase.serializeFields(BeanSerializerBase.java:774) ~[jackson-databind-2.13.4.2.jar:2.13.4.2]
    at com.fasterxml.jackson.databind.ser.BeanSerializer.serialize(BeanSerializer.java:178) ~[jackson-databind-2.13.4.2.jar:2.13.4.2]
    at com.fasterxml.jackson.databind.ser.BeanPropertyWriter.serializeAsField(BeanPropertyWriter.java:728) ~[jackson-databind-2.13.4.2.jar:2.13.4.2]
    at com.fasterxml.jackson.databind.ser.std.BeanSerializerBase.serializeFields(BeanSerializerBase.java:774) ~[jackson-databind-2.13.4.2.jar:2.13.4.2]

lots of line.............

我已經在 gitHub 上上傳了這個專案：https ://github.com/aniketkadu0/hms_new.git

旅舍.java

@Table(name = "hostels")
public class Hostel implements Cloneable {
    
    @Id
    @GeneratedValue(strategy=GenerationType.IDENTITY)
    int hostelId;
    String hostelName;
    String hostelAddress;
    String contactPersonName;
    String contactPersonNumber;
    
    @OneToMany
    @JoinTable(joinColumns = @JoinColumn(
            name = "hostel_id",
            referencedColumnName = "hostelId"
    ),
    inverseJoinColumns = @JoinColumn(
            name = "room_number",
            referencedColumnName = "roomNumber"
    ))
    List<Room> rooms;
    @OneToOne
    Mess mess;
    @OneToMany
    List<Notice> notices;
    
}

房間.java

@Table(name = "rooms")
public class Room {
    
    @Id
    int roomNumber;
    int noOfOccupants;
    @OneToOne
    RoomDetail roomDetail;
    @OneToOne
    Hostel hostel;
    @OneToMany
    List<Student> student;
    
}

RoomDetail.java

@Entity
public class RoomDetail {
    
    @Id
    @GeneratedValue(strategy=GenerationType.IDENTITY)
    int roomDetailId;
    String roomName;
    int price;
    int maxOccupants;
}

旅館 JSON

{
    "hostelId": 1,
    "hostelName": "Hostel no. 1 Boys Hostel",
    "hostelAddress": "building no. 5",
    "contactPersonName": "XYZ",
    "contactPersonNumber": "9999977777",
    "rooms": null,
    "mess": null,
    "notices": null
}

房間 JSON

{
    "noOfOccupants" : 0,
    "roomDetail" : {
        "roomDetailId" : 1
    } ,
    "hostel" : {
        "hostelId" : 1
    }
}

管理服務.java

@Service
public class AdminService {

    @Autowired
    HostelDAO hostelDAO;
    @Autowired
    RoomDAO roomDAO;
    @Autowired
    RoomDetailDAO roomDetailDAO;

    public Hostel addHostel(Hostel hostel) {
        return hostelDAO.save(hostel);
    }

    public Room addRoom(Room room,int qty,int firstRoomNumber){
        
        Optional<Hostel> hostel = hostelDAO.findById(room.getHostel().getHostelId());   
        Optional<RoomDetail> roomDetail = roomDetailDAO.findById(room.getRoomDetail().getRoomDetailId());
        
        room.setHostel(hostel.get());
        room.setRoomDetail(roomDetail.get());
        
        List<Room> rooms = new ArrayList<>();   
        room.setRoomNumber(firstRoomNumber);
        System.out.println(room);
                
        firstRoomNumber--;
        int i = 1;
        while( i <= qty) {
            Room newRoom = new Room(room.getRoomNumber(),
                                    room.getNoOfOccupants(),room.getRoomDetail(),
                                    room.getHostel(),room.getStudent());
            newRoom.setRoomNumber(firstRoomNumber   i);
            rooms.add(newRoom);
            i  ;    
        }

        roomDAO.saveAll(rooms);
        hostel.get().setRooms(rooms);
        hostelDAO.save(hostel.get());
        return null;
    }

    public List<Hostel> getHostelData() {
        return hostelDAO.findAll();
    }

}

uj5u.com熱心網友回復：

序列化 Hostel 的問題在于您的 Hostel 的房間指向同一個 Hostel。有很多方法可以告訴您的 JSON 序列化程式如何處理它。假設您使用的是 Jackson，最簡單的方法可能是在不需要序列化的一側添加 @JsonIgnore 注釋。IE：

@Table(name = "rooms")
public class Room {
    
    @Id
    int roomNumber;
    int noOfOccupants;
    @OneToOne
    RoomDetail roomDetail;
    @OneToOne
    @JsonIgnore
    Hostel hostel;
    @OneToMany
    List<Student> student;   
}

您將不得不查看所有回圈參考——實際上是整個圖表——并決定在通過 REST 呼叫獲取時您真正想要序列化的內容，以及您的客戶端可能需要如何處理資料。

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