java - 删除两个对象之间的关联

Question

我在 Spring 中创建应用程序，它存储专辑、音乐家和乐队。专辑可以包含多个乐队和音乐家。我在 Album 和 Band/Musician 之间创建了关联。 Jet 我无法删除它。我不想删除对象，只想删除关联。我尝试发送 REST PUT 请求并将 Album 站点上的 musicians 和 bands 设置为 null，但没有任何反应:

{
        "id": 2,
        "title": "Lulu",
        "bands": null,
        "musicians": null,
        "duration": {
            "hours": 1,
            "minutes": 20,
            "seconds": 4
        },
        "releaseDate": "31/10/2011",
        "coverPath": "https://upload.wikimedia.org/wikipedia/en/4/40/Lou_Reed_and_Metallica_-_Lulu.jpg",
        "spotifyPath": null
}

我创建了以下类和方法来链接 Album 和 Musician，但我无法“取消链接”它们:

@RestController
public class AlbumMusicianController {
    @Autowired
    AlbumRepository albumRepository;
    @Autowired
    MusicianRepository musicianRepository;

    @Transactional
    @PostMapping("/musician/{musicianId}/album/{albumId}")
    public List<Album> associate(@PathVariable Long musicianId, @PathVariable Long albumId) {
        Album album = this.albumRepository.findById(albumId).orElseThrow(() -> new MissingResourceException("Album",
                "Album", albumId.toString()));

        return this.musicianRepository.findById(musicianId).map((musician) -> { musician.getAlbums().add(album);
            return this.musicianRepository.save(musician).getAlbums();
        }).orElseThrow(() -> new MissingResourceException("Musician", "Musician", musicianId.toString()));
    }
}

非常感谢您的帮助。

以下是必要的来源。

相册类:

@Entity
@Table(name="album")
@JsonIdentityInfo(
        generator = ObjectIdGenerators.PropertyGenerator.class,
        property = "id")
public class Album {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long id;
    @Column(name="title")
    private String title;
    @ManyToMany(targetEntity = Band.class, mappedBy = "albums")
    @JsonSerialize(using = BandsSerializer.class)
    private List<Band> bands;
    @ManyToMany(targetEntity = Musician.class, mappedBy = "albums")
    @JsonSerialize(using = MusiciansSerializer.class)
    private List<Musician> musicians;
    @Embedded
    @Column(name="duration")
    private Duration duration;
    @Column(name="releasedate")
    @JsonFormat(shape=JsonFormat.Shape.STRING, pattern="dd/MM/yyyy", timezone="CET")
    private Date releaseDate;
    @Column(name="coverpath")
    private String coverPath;
    @Column(name="spotifypath")
    private String spotifyPath;
    public Long getId() {
        return id;
    }
    public void setId(Long id) {
        this.id = id;
    }
    public String getTitle() {
        return title;
    }
    public void setTitle(String title) {
        this.title = title;
    }
    public Duration getDuration() {
        return duration;
    }
    public void setDuration(Duration duration) {
        this.duration = duration;
    }
    public Date getReleaseDate() {
        return releaseDate;
    }
    public void setReleaseDate(Date releaseDate) {
        this.releaseDate = releaseDate;
    }
    public String getCoverPath() {
        return coverPath;
    }
    public void setCoverPath(String coverPath) {
        this.coverPath = coverPath;
    }
    public String getSpotifyPath() {
        return spotifyPath;
    }
    public void setSpotifyPath(String spotifyPath) {
        this.spotifyPath = spotifyPath;
    }
    public List<Band> getBands() {
        return bands;
    }
    public void setBands(List<Band> bands) {
        this.bands = bands;
    }
    public List<Musician> getMusicians() {
        return musicians;
    }
    public void setMusicians(List<Musician> musicians) {
        this.musicians = musicians;
    }
}

音乐家类:

@Entity
@Table(name="musician")
@JsonIdentityInfo(
        generator = ObjectIdGenerators.PropertyGenerator.class,
        property = "id")
public class Musician {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long id;
    @Column(name="name")
    private String name;
    @Column(name="surname")
    private String surname;
    @Column(name="birthdate")
    @JsonFormat(shape=JsonFormat.Shape.STRING, pattern="dd/MM/yyyy", timezone="CET")
    private Date birthDate;
    @Column(name="picturepath")
    private String picturePath;
    @ManyToMany(cascade = CascadeType.ALL)
    @JoinTable(name = "album_musician",
            joinColumns = @JoinColumn(name = "album_id", referencedColumnName = "id"),
            inverseJoinColumns = @JoinColumn(name = "musician_id",
                    referencedColumnName = "id"))
    private List<Album> albums;
    public Long getId() {
        return id;
    }
    public void setId(Long id) {
        this.id = id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public String getSurname() {
        return surname;
    }
    public void setSurname(String surname) {
        this.surname = surname;
    }
    public Date getBirthDate() {
        return birthDate;
    }
    public void setBirthDate(Date birthDate) {
        this.birthDate = birthDate;
    }
    public String getPicturePath() {
        return picturePath;
    }
    public void setPicturePath(String picturePath) {
        this.picturePath = picturePath;
    }
    public List<Album> getAlbums() {
        return albums;
    }
    public void setAlbums(List<Album> albums) {
        this.albums = albums;
    }
}

乐队类:

@Entity
@Table(name="band")
@JsonIdentityInfo(
        generator = ObjectIdGenerators.PropertyGenerator.class,
        property = "id")
public class Band {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long id;
    @Column(name="name")
    private String name;
    @Column(name="picturepath")
    private String picturePath;
    @ManyToMany(cascade = CascadeType.ALL)
    @JoinTable(name = "album_band",
            joinColumns = @JoinColumn(name = "album_id", referencedColumnName = "id"),
            inverseJoinColumns = @JoinColumn(name = "band_id",
                    referencedColumnName = "id"))
    @JsonSerialize(using = AlbumsSerializer.class)
    private List<Album> albums;
    public Long getId() {
        return id;
    }
    public void setId(Long id) {
        this.id = id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public String getPicturePath() {
        return picturePath;
    }
    public void setPicturePath(String picturePath) {
        this.picturePath = picturePath;
    }
    public List<Album> getAlbums() {
        return albums;
    }
    public void setAlbums(List<Album> albums) {
        this.albums = albums;
    }
}

Answer 1

根据您的 JSON 正文，我假设您正在发送针对相册实体的 PUT 请求。我发现有两件事在调整后对我有用。我不确定您是否出于某种原因避免使用它们。

• 级联规则将相册的更改级联到其关系。
• 从相册到其关系的连接表的正确实体映射。
  • 不太确定为什么这是一个问题 - Hibernate 在执行时似乎没有抛出任何与此相关的异常，但它似乎没有正确地持久化事物。

这是专辑与音乐家关系的调整后的关系定义。

@ManyToMany(cascade = CascadeType.ALL)
@JoinTable(name="album_musician", joinColumns = @JoinColumn(name = "musician_id", referencedColumnName = "id"),
inverseJoinColumns = @JoinColumn(name = "album_id",
        referencedColumnName = "id"))
private List<Musician> musicians;

在这种格式中，我能够将专辑中的更改级联到音乐家。您必须对 Band 实体执行类似的操作，才能将操作从专辑级联到 Band。