在SpringbootJPA中以多對多關系訪問@JoinTable

我創建了一個包含演員、電影和類別物體的 API。演員和電影通過映射到名為movie_actor的連接表的多對多關系連接，類別通過一對多關系與電影連接。

我正在嘗試撰寫一個本機查詢，該查詢回傳一個整數，該整數表示特定演員播放過的特定類別的電影數量，例如，如果演員在 2 部不同的科幻電影中播放，查詢將回傳 2。從資料庫級別執行此操作沒有問題，我可以看到連接表movie_actor，但該表在我的api中仍然無法訪問，因為它不是一個單獨的物體。如何創建它以自動將演員和電影 ID 映射為 movie_actor 表？

這是在 H2 資料庫中為我作業的示例代碼：

SELECT COUNT(*) FROM MOVIE M JOIN MOVIE_ACTOR MA on M.MOVIE_ID = MA.MOVIE_ID WHERE ACTOR_ID = 1 AND CATEGORY_ID = 1

這是我的物體：

演員：

@Entity
@Data
@Table(name = "actor")
@AllArgsConstructor
@NoArgsConstructor
public class Actor {

@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
@Column(name = "actor_id")
private long actorId;

@Column(name = "name")
private String name;

@Column(name = "surname")
private String surname;

@Nullable
@ManyToMany(mappedBy = "actors", fetch = FetchType.EAGER)
@JsonBackReference
private List<Movie> movies = new ArrayList<>();

public Actor(String name, String surname){
    this.name = name;
    this.surname = surname;
}
}

電影：

@Entity
@Data
@Table(name = "movie")
@AllArgsConstructor
@NoArgsConstructor
public class Movie {

@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
@Column(name = "movie_id")
private long movieId;

@Column(name = "title")
private String title;

@ManyToMany
@JoinTable(
        name = "movie_actor",
        joinColumns = @JoinColumn(name = "movie_id"),
        inverseJoinColumns = {@JoinColumn(name = "actor_id")}
)
@JsonManagedReference
private List<Actor> actors = new ArrayList<>();

@ManyToOne
@JoinColumn(name = "CATEGORY_ID")
@JsonManagedReference
private Category category;
}

uj5u.com熱心網友回復：

所以你必須讓它在你的 API 中可以訪問。一種選擇是將交集表映射movie_actor到物體，然后將關系MovieActor拆分為和之間的關系，如下所示：ManyToManyActorMovieOneToManyMovieActor

@Entity
@Data
@Table(name = "movie_actor")
@AllArgsConstructor
@NoArgsConstructor
public class MovieActor {
    @EmbeddedId
    private MovieActorId productOrderId = new MovieActorId();

    @ManyToOne(cascade = CascadeType.ALL, optional = false)
    @MapsId("movieId")
    @JoinColumn(name = "product_id", nullable = false)
    private Movie movie;

    @ManyToOne(cascade = CascadeType.ALL, optional = false)
    @MapsId("actorId")
    @JoinColumn(name = "order_id", nullable = false)
    private Actor actor;

    public void addMovieActor(Movie aMovie, Actor aActor) {
        movie = aMovie;
        actor = aActor;

        aMovie.getMovieActors().add(this);
        aActor.getMovieActors().add(this);
    }
}

@Embeddable
@Getter
@Setter
public class MovieActorId  implements Serializable {
    @Column(name = "movie_id")
    private Long movieId;

    @Column(name = "actor_id")
    private Long actorId;
}

@Entity
@Data
@Table(name = "actor")
@AllArgsConstructor
@NoArgsConstructor
public class Actor {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "actor_id")
    private long actorId;

    @OneToMany(mappedBy = "actor")
    private List<MovieActor> movieActors = new ArrayList<>();
}

@Entity
@Data
@Table(name = "movie")
@AllArgsConstructor
@NoArgsConstructor
public class Movie {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "movie_id")
    private long movieId;

    @OneToMany(mappedBy = "movie")
    private List<MovieActor> movieActors = new ArrayList<>();
}

現在您可以訪問查詢中的交集表MovieActor。如果需要，您甚至可以在此表中添加更多列。

標籤：爪哇 弹簧靴 jpa 弹簧数据-jpa h2

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