Spring-boot JPA无限循环多对多

Question

我有两个实体，它们是多对多关系。

@Entity
public class Room {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private long id;

    @ManyToMany(mappedBy = "rooms")
    private Set<Team> teams;
}

@Entity
public class Team {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private long id;

    @ManyToMany
    @JoinTable(name = "teams_rooms",
        joinColumns = @JoinColumn(name= "team_id"),
        inverseJoinColumns = @JoinColumn(name = "room_id"))
    private Set<Room> rooms;

}

为了产生数据，我有一个“房间”和“团队”的存储库：

public interface RoomRepository extends CrudRepository<Room, Long> {
}

public interface TeamRepository extends CrudRepository<Team, Long> {
}

我的目标是请求团队的所有房间，但防止 JPA 无限循环。

@RestController
@RequestMapping("....")
public class RoomController {
    @Autowired
    private RoomRepository roomRepository;
    
    @GetMapping
    public Iterable<Room> getAllRoomsOfTeam() {
        final long exampleId = 1; //This is just a placeholder. The id will be passed as a parameter.
        
        final var team = teamRepository.findById(exampleId);

        return ResponseEntity.ok(team);
    }
}

这是结果：

{
    "id": 1,
    "name": "Team1",
    "rooms": [
        {
            "id": 1,
            "name": "Room 1",
            "teams": [
                {
                    "id": 1,
                    "name": "Team 1",
                    "rooms": [
                        {
                            "id": 1,
                            "name": "Room 1",
                            "teams": [

Jackson 将永远循环，直到发生异常（因为反向引用也引用了父元素，这将创建一个循环）。 我已经尝试过@JsonManagedReference 和@JsonBackReference，但它们用于多对一关系。

如何阻止杰克逊无限循环？我想尽可能少地影响其他存储库和查询。

Answer 1

目前，您的类中存在循环依赖，这在将对象转换为 JSON 时会导致问题。请在Team 类中的rooms 变量上添加@JsonIgnore 注释，如下例所示：

import com.fasterxml.jackson.annotation.JsonIgnore;

@Entity
public class Team {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private long id;

    @ManyToMany
    @JoinTable(name = "teams_rooms",
        joinColumns = @JoinColumn(name= "team_id"),
        inverseJoinColumns = @JoinColumn(name = "room_id"))
    @JsonIgnore
    private Set<Room> rooms;

}

---

如果您需要双向转换的解决方案，则可以使用JsonView 注解。

首先，您需要为Team 和Room 创建JSON 视图配置文件，如下例所示：

public class JsonViewProfiles
{
    /**
     * This profile will be used while converting Team object to JSON
     */
    public static class Team {}

    /**
     * This profile will be used while converting Room object to JSON
     */
    public static class Room {}
}

在您的实体中使用上面创建的 JSON 视图配置文件，如下例所示：

public class Room {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    @JsonView({ JsonViewProfiles.Team.class, JsonViewProfiles.Room.class })
    private long id;

    @JsonView(JsonViewProfiles.Room.class)
    @ManyToMany(mappedBy = "rooms")
    private Set<Team> teams;
}

public class Team {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    @JsonView({JsonViewProfiles.Team.class, JsonViewProfiles.Room.class})
    private long id;

    @ManyToMany
    @JoinTable(name = "teams_rooms",
        joinColumns = @JoinColumn(name= "team_id"),
        inverseJoinColumns = @JoinColumn(name = "room_id"))
    @JsonView(JsonViewProfiles.Team.class)
    private Set<Room> rooms;
}

在将您的对象转换为 JSON 时，请使用这些配置文件，如下例所示：

@GetMapping
public String getAllRoomsOfTeam() {
    final long exampleId = 1; //This is just a placeholder. The id will be passed as a parameter.

    final Team team = teamRepository.findById(exampleId);

    String result = new ObjectMapper().writerWithView(JsonViewProfiles.Team.class)
                .writeValueAsString(team);

    return result;
}

Answer 2

您的控制器不应返回 entities（带有注释 @Entity 的类）。最佳实践是创建另一个具有相同属性的单独类。这段代码有一些重复，但它使所有层保持干净。我也建议使用@Service。

   public class RoomDTO { 
       private String name;
       private List<TeamDTO> teams = new ArrayList<>();   

       public RoomDTO() { 
       }
        
       public RoomDTO(Room room) {
            this.name = room.name;
            for(Team team : room.getTeams()) {
                 TeamDTO teamDTO = new TeamDTO();
                 teamDTO.setName(team.getName);
                 teams.add(teamDTO);
            }
        }
   }



   public class TeamDTO { 
       List<RoomDTO> rooms = new ArrayList();

       public TeamDTO() {
       }

       public TeamDTO(Team team) {
            this.name = team.name;
            for(Room room : team.getRooms()) {
                 RoomDTO roomDTO = new RoomDTO();
                 roomDTO.setName(team.getName);
                 rooms.add(roomDTO);
            }
        }
        
   }

控制器应该返回这个

@GetMapping
public Iterable<TeamDTO> getAllRoomsOfTeam() {
final long exampleId = 1;
final var team = teamRepository.findById(exampleId);

TeamDTO teamDTO = new TeamDTO(team);

return ResponseEntity.ok(teamDTO);

}

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