JPA 和 Hibernate、OneToMany 关系与使用 UUID 的复合键

Question

我正在使用带有 JPA 和 Hibernate 的 SpringBoot。

我有两个实体：书和作者。一本书可以有多个作者。所以我需要一个 OneToMany 关系。

进入 Author 表，我的想法是使用复合键（book_id 和一个内部字段，例如 field_a）

我实现了这些类：

@Entity
@Table(name = "book")
public class Book extends MyBaseEntity {

    @Id
    @Column(name = "id")
    @Type(type = "uuid-char")
    private UUID uuid = UUID.randomUUID();

    @Column(name = "name", nullable = false)
    private String name;

    @OneToMany(mappedBy = "book")
    private List<Author> authors = new ArrayList<>();

}

@Entity
@Table(name = "author")
public class Author extends MyBaseEntity {

    @EmbeddedId
    private CustomID id;

    @ManyToOne()
    @MapsId("bookId")
    @JoinColumn(name = "book_id")
    private Book book;

    @Column(name = "field_a", nullable = false)
    @MapsId("fieldA")
    @Type(type = "uuid-char")
    private UUID fieldA;

}


@Embeddable
public class CustomID implements Serializable {

    @Column(name = "book_id")
    private UUID bookId;

    @Column(name = "field_a")
    private UUID fieldA;

    public CustomID() { }

    public CustomID(UUID bookId, UUID fieldA) {
        this.bookId = bookId;
        this.fieldA = fieldA;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;

        if (o == null || getClass() != o.getClass())
            return false;

        ShareID that = (CustomID) o;
        return Objects.equals(bookId, that.bookId) &&
                Objects.equals(fieldA, that.fieldA);
    }

    @Override
    public int hashCode() {
        return Objects.hash(bookId, fieldA);
    }
}

当我尝试执行我的项目时（我正在使用属性spring.jpa.hibernate.ddl-auto=create 生成数据库）我收到此错误：

ERROR SpringApplication-reportFailure():837 - [ Application run failed ]
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: Unknown entity name: java.util.UUID 

有什么建议吗？

如果我尝试删除组合键的使用效果很好，那么问题可能与组合键的实现或使用有关。

Answer 1

使用带有 Author as 的 ID 类：

@Entity
@Table(name = "author")
@IdClass(CustomID.class)
public class Author extends MyBaseEntity {

    @Id
    @ManyToOne()
    @JoinColumn(name = "book_id")
    private Book book;

    @ID
    @Column(name = "field_a", nullable = false)
    @Type(type = "uuid-char")
    private UUID fieldA;

}

public class CustomID implements Serializable {
    //these match the names of the property marked with @Id in Author
    private UUID book;
    private UUID fieldA;
}

或者像您已经完成的那样为您的实体定义基本字段的嵌入：

@Entity
@Table(name = "author")
public class Author extends MyBaseEntity {

    @EmbeddedId
    private CustomID id;

    @ManyToOne()
    @MapsId("bookId")
    @JoinColumn(name = "book_id")
    private Book book;
}