java - 为什么当我尝试在数据库中插入新对象时出现错误？

Question

我的场景如下

一个User可以有一个Track列表，与之对应，Track实体包含一个用户id。(@一对多)

每当创建新轨道时，轨道列表都会更新。

上述实体如下:

Track Entity

@Entity
@Table(name ="track")
public class Track {
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private Long trackId;

@ManyToOne
@JoinColumn(name = "userId", nullable = false)
private User user;

@OneToOne(mappedBy = "track")
private Share share;

private String trackName;

@OneToMany(mappedBy = "pointId")
private List<Point> point;

@OneToOne(mappedBy = "track")
private TrackStatistic trackStatistic;

User Entity

@Entity
@Table(name = "user")
public class User {

@Id
@GeneratedValue(strategy=GenerationType.AUTO)
@Column(name = "USER_ID")
private Long id;

private String firstName;

private String lastName;

@Column(unique = true)
private String username;

private String password;

@Column(unique = true)
private String email;

@Column(unique = true)
private String phoneNumber;

private int age;

private Role role;

@OneToMany(mappedBy = "shareId")
private List<Share> shares;

@OneToMany(mappedBy = "trackId")
private List<Track> tracks;

}

createTrack method is as follows

public Track createTrack(String username, TrackDTO trackDTO) {
    //Find user
    User user = userRepository.findByUsername(username);

    //Convert Dto to Entity
    Track track = modelMapper.map(trackDTO, Track.class);

    //Update user track list
    user.getTracks().add(track);

    //Update track
    track.setUser(user);

    //save user
    userRepository.save(user);

    //save track
    return trackRepository.save(track);
}

注意，TrackDTO是Track实体对应的Dto类

<小时/>

当我运行createTrack时，我遇到了以下错误:

2020-01-18 20:48:23.315 ERROR 14392 --- [nio-8080-exec-1] o.h.engine.jdbc.spi.SqlExceptionHelper:
 Cannot add or update a child row: a foreign key constraint fails (`thdb`.`track`, CONSTRAINT `FK5cftk3hw8vfnaigtj063skvxs` FOREIGN KEY (`track_id`) REFERENCES `user` (`user_id`))

2020-01-18 20:48:23.338 ERROR 14392 --- [nio-8080-exec-1] o.a.c.c.C.[.[.[/].[dispatcherServlet]:
 Servlet.service() for servlet [dispatcherServlet] in context with path [] threw exception [Request processing failed; nested exception is org.springframework.dao.DataIntegrityViolationException: could not execute statement; SQL [n/a]; constraint [null]; nested exception is org.hibernate.exception.ConstraintViolationException: could not execute statement] with root cause

java.sql.SQLIntegrityConstraintViolationException: Cannot add or update a child row: a foreign key constraint fails 
(`thdb`.`track`, CONSTRAINT `FK5cftk3hw8vfnaigtj063skvxs` FOREIGN KEY (`track_id`) REFERENCES `user` (`user_id`))

Answer 1

已编辑

<小时/>

通过主动级联，当您保存User时，无需再次保存Track。所以我对您的代码做了一些更改，如下所示，希望它有所帮助

1- Add cascade = CascadeType.ALL to User entity

2- Add targetEntity = Track .class, mappedBy = "user" to User entity

3- Add @ManyToOne(targetEntity = User.class) @JoinColumn(name = "USER_FK") to Track entity

4-Delete trackRepository.save(track);

5- Just save user(userRepository.save(user)). by cascade, it saves the track too.

6- Return the last track in user list.(Newest saved track)

<小时/>

我对上述编辑进行了编码，如下

User Entity

@Entity
@Table(name = "user")
public class User {

  //other properties

   @OneToMany(targetEntity = Track.class , mappedBy = "user" ,cascade = CascadeType.ALL)
   private List<Track> tracks;

   //getters and setters   
  
  }

Track Entity

@Entity
@Table(name ="track")
public class Track {
 
//other properties

@ManyToOne(targetEntity = User.class)
@JoinColumn(name = "USER_FK",nullable = false)
private User user;

//getters and setters

}

createTrack method

public Track createTrack(String username, TrackDTO trackDTO) {

    //Find user
    User user = userRepository.findByUsername(username);

    //Convert Dto to Entity
    Track track = modelMapper.map(trackDTO, Track.class);

    //Update User and Track
    user.getTracks().add(track);
    track.setUser(user);

    //save user
    User result = userRepository.save(user);
    
    //find saved track (you can fetch track by other ways too)
    Track savedTrack = result.getTracks().get(result.getTracks().size()-1);

    return savedTrack;
}