Question

我在与JPA的多对多关系中遇到麻烦。我的代码如下：

传感器类：

@Entity
@Table(name = "sensor")
@Data
@NoArgsConstructor
@AllArgsConstructor
public class Sensor {
    @Id
    private long chipId;
    @OneToMany(mappedBy = "sensor")
    @JsonBackReference
    private Set<Link> userLinks;
    private String firmwareVersion;
    private long creationTimestamp;
    private String notes;
    private long lastMeasurementTimestamp;
    private long lastEditTimestamp;
    private double gpsLatitude;
    private double gpsLongitude;
    private double gpsAltitude;
    private String country;
    private String city;
    private boolean indoor;
    private boolean published;
}

用户类别：

@Entity
@Table(name = "user")
@Data
@NoArgsConstructor
@AllArgsConstructor
public class User {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @JsonManagedReference
    private int id;
    private String firstName;
    private String lastName;
    private String email;
    private String password;
    @OneToMany(mappedBy = "user")
    private Set<Link> sensorLinks;
    private int role;
    private int status;
    private long creationTimestamp;
    private long lastEditTimestamp;
}

和Link类（关系类）：

@Entity
@Table(name = "link")
@Data
@AllArgsConstructor
@NoArgsConstructor
public class Link {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Integer id;

    @ManyToOne
    @JoinColumn(name = "user_id")
    @MapsId("user_id")
    private User user;

    @ManyToOne
    @JoinColumn(name = "sensor_id")
    @MapsId("sensor_id")
    private Sensor sensor;

    private boolean owner;
    private String name;
    private int color;
    private long creationTimestamp;
}

控制器：

...

@RequestMapping(method = RequestMethod.GET, path = "/user/{email}", produces = MediaType.APPLICATION_JSON_VALUE)
@ApiOperation(value = "Returns details for one specific user")
public User getUserByEmail(@PathVariable("email") String email) {
    return userRepository.findByEmail(email).orElse(null);
}

...

UserRepository：

public interface UserRepository extends JpaRepository<User, Integer> {

    Optional<User> findByEmail(String email);

    @Modifying
    @Query("UPDATE User u SET u.firstName = ?2, u.lastName = ?3, u.password = ?4, u.role = ?5, u.status = ?6 WHERE u.id = ?1")
    Integer updateUser(int id, String firstName, String lastName, String password, int role, int status);
}

我想实现，用户端点显示与该特定用户的所有链接传感器。我得到的只是一条错误消息：

JSON映射问题： com.chillibits.particulatematterapi.model.db.main.User [“ sensorLinks”]; 嵌套异常为 com.fasterxml.jackson.databind.JsonMappingException：无限递归（StackOverflowError）（通过参考链： com.chillibits.particulatematterapi.model.db.main.User [“ sensorLinks”]）

如何解决此问题？

预先感谢

马克

------------------------------------编辑---------- -------------------------

根据Abinash Ghosh的回答，我添加了以下DTO：

UserDto：

@Data
@NoArgsConstructor
@AllArgsConstructor
public class UserDto {
    private int id;
    private String firstName;
    private String lastName;
    private Set<LinkDto> sensorLinks;
    private int role;
    private int status;
    private long creationTimestamp;
    private long lastEditTimestamp;
}

LinkDto：

@Data
@NoArgsConstructor
@AllArgsConstructor
public class LinkDto {
    private Integer id;
    private SensorDto sensor;
    private boolean owner;
    private String name;
    private int color;
    private long creationTimestamp;
}

和映射器（我意识到它有些不同，但是应该相同）：

public UserDto getUserByEmail(@PathVariable("email") String email) {
    User user = userRepository.findByEmail(email).orElse(null);
    return convertToDto(user);
}

private UserDto convertToDto(User user) {
    return mapper.map(user, UserDto.class);
}

这导致以下异常：

2020-04-13 14:22:24.383  WARN 8176 --- [nio-8080-exec-2] o.h.e.loading.internal.LoadContexts      : HHH000100: Fail-safe cleanup (collections) : org.hibernate.engine.loading.internal.CollectionLoadContext@68ab57c7<rs=HikariProxyResultSet@2017009664 wrapping Result set representing update count of -1>

1) Error mapping com.chillibits.particulatematterapi.model.db.main.User to com.chillibits.particulatematterapi.model.io.UserDto
1 error] with root cause
java.lang.StackOverflowError: null
at com.mysql.cj.NativeSession.execSQL(NativeSession.java:1109) ~[mysql-connector-java-8.0.19.jar:8.0.19]
...

Answer 1

当@types/react-router@3.0.22序列化响应时，将调用User字段的所有getter方法。因此，也调用User关系字段User的getter来设置值。这是递归发生的。那是无限递归的原因。

最好不要使用Entity作为响应。为sensorLinks创建一个DTO类，然后将User实体值映射到DTO中，然后发送响应。 不要在DTO中再次使用任何Enity类，这样会导致同样的问题

要动态地将一个模型映射到另一个模型，可以使用User

ModleMapper

Answer 2

正在工作！这篇文章对您有帮助：https://stackoverflow.com/a/57111004/6296634

在这种情况下，您似乎不应该使用Lombok @Data。

JPA：多对多关系-JsonMappingException：无限递归

2 个答案: