如何映射此复合主键？

Question

我正在使用 spring 创建一个社交媒体网站，但我遇到了复合主键的问题。 我有 User、Post 和 PostLike 表，我需要跟踪哪些用户喜欢哪些帖子。我还有一个 UserData 和 Post 关系，它告诉我帖子作者，但这不会造成任何问题。基本上，我的 PostLike 表应该包含 post_id 和 user_id 列，它们应该用作复合主键。

我试图通过创建一个可嵌入的 PostLikeId 来做到这一点：

我的 PostLikeId 类：

@Embeddable
public class PostLikeId implements Serializable {

    @Column(name = "post_id")
    private Post post;

    @Column(name = "user_id")
    private UserData user;

    // getters and setters

}

我的 PostLike 类：

@Entity
@Table(name = "post_like")
public class PostLike {

    @EmbeddedId
    private PostLikeId id;

    //getters and setters
}

我的帖子类：

@Entity
@Table(name = "post")
public class Post {

    @Id
    @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "post_id_seq_generator")
    @SequenceGenerator(name = "post_id_seq_generator", sequenceName = "post_id_seq", allocationSize = 10)
    @Column(name = "id", updatable = false)
    private Long id;

    @OneToMany(cascade = CascadeType.ALL,
            orphanRemoval = true
    )
    @JoinColumns({
            @JoinColumn(name = "post_id",
                    referencedColumnName = "post_id"),
            @JoinColumn(name = "user_id",
                    referencedColumnName = "user_id")
    })
    private List<PostLike> likes = new ArrayList<>();

}

...和我的 UserData 类：

@Entity
@Table(name = "user_data")
public class UserData {

    @Id
    @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "user_data_id_seq_generator")
    @SequenceGenerator(name = "user_data_id_seq_generator", sequenceName = "user_data_id_seq", allocationSize = 10)
    @Column(name = "id", updatable = false)
    private Long id;

    @OneToMany(
            mappedBy = "user",
            cascade = CascadeType.ALL,
            orphanRemoval = true
    )
    private List<Post> posts = new ArrayList<>();

    @OneToMany(
            mappedBy = "id",
            cascade = CascadeType.ALL,
            orphanRemoval = true
    )
    private List<PostLike> likedPosts = new ArrayList<>();

当我尝试运行和映射它时，我得到以下异常：

org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'entityManagerFactory' defined in class path resource [org/springframework/boot/autoconfigure/orm/jpa/HibernateJpaConfiguration.class]: Invocation of init method failed; nested exception is org.hibernate.AnnotationException: Unable to map collection com.budano.SocialStudent.model.Post.likes
.
.
.
Caused by: org.hibernate.AnnotationException: Unable to map collection com.budano.SocialStudent.model.Post.likes
.
.
.
Caused by: org.hibernate.cfg.RecoverableException: Unable to find column with logical name: post_id in org.hibernate.mapping.Table(public.post) and its related supertables and secondary tables

谁能解释一下这个日志告诉我什么以及我应该如何解决这个问题？ 谢谢！

Answer 1

这是您可以尝试的方法：

PostLikeId：

@Embeddable
public class PostLikeId implements Serializable {

    @Column(name = "post_id")
    private Long postId; // corresponds to PK type of Post

    @Column(name = "user_id")
    private Long userId; // corresponds to PK type of User

    // ...

}

点赞：

@Entity
@Table(name = "post_like")
public class PostLike {

    @EmbeddedId
    private PostLikeId id;

    @MapsId("postId") // maps postId attribute of embedded id
    @ManyToOne
    private Post post;

    @MapsId("userId") // maps userId attribute of embedded id
    @ManyToOne
    private UserData user;

    // ...
}

帖子：

@Entity
@Table(name = "post")
public class Post {

    @Id
    @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "post_id_seq_generator")
    @SequenceGenerator(name = "post_id_seq_generator", sequenceName = "post_id_seq", allocationSize = 10)
    @Column(name = "id", updatable = false)
    private Long id;

    @ManyToOne
    private UserData user;

    @OneToMany(mappedBy = "post", cascade = CascadeType.ALL, orphanRemoval = true)
    private List<PostLike> likes = new ArrayList<>();

    // ...
}

用户数据：

@Entity
@Table(name = "user_data")
public class UserData {

    @Id
    @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "user_data_id_seq_generator")
    @SequenceGenerator(name = "user_data_id_seq_generator", sequenceName = "user_data_id_seq", allocationSize = 10)
    @Column(name = "id", updatable = false)
    private Long id;

    @OneToMany(mappedBy = "user", cascade = CascadeType.ALL, orphanRemoval = true)
    private List<Post> posts = new ArrayList<>();

    @OneToMany(mappedBy = "user", cascade = CascadeType.ALL, orphanRemoval = true)
    private List<PostLike> likedPosts = new ArrayList<>();

    // ...
}

在第 2.4.1 节的JPA 2.2 spec 中讨论了派生的身份（带有示例）。