Question

我有三个表：

CREATE TABLE book (
 id BIGINT(20) UNSIGNED NOT NULL AUTO_INCREMENT,
 title VARCHAR(256),
 ...
 PRIMARY KEY (`id`)
)

CREATE TABLE book_extras (
 id BIGINT(20) unsigned NOT NULL AUTO_INCREMENT,
 book_extra_type VARCHAR(20),  
 book_id INT NOT NULL,
 ...
 PRIMARY KEY(id),
 KEY fk_book_extras_books (book_id),
 CONSTRAINT fk_book_extras_book FOREIGN KEY (book_id) REFERENCES book (id) ON DELETE CASCADE ON 
   UPDATE CASCADE
)

CREATE TABLE book_cd (
 id BIGINT(20) unsigned NOT NULL,
 singer VARCHAR(100) NOT NULL,
 ...
 PRIMARY KEY (`id`),
 CONSTRAINT `FK_book_cd_book_extras` FOREIGN KEY (`id`)
  REFERENCES `book_extras` (`id`) ON DELETE CASCADE ON UPDATE CASCADE
)

对于每个表，我都有一个实体类：

@Entity
@Table(name = "book")
@Data
@Builder
@NoArgsConstructor
@AllArgsConstructor
public class Book{
  @Id
  @GeneratedValue(strategy = GenerationType.IDENTITY)
  private Long id;

  @OneToMany(mappedBy = "book")
  private List<BookExtra> bookExtras;

  @OneToMany(mappedBy = "book", cascade = CascadeType.ALL)
  private List<BookCd> cds= new ArrayList<>();
  ...
}

@Entity
@Table(name = "book_extras")
@Inheritance(strategy = InheritanceType.JOINED)
@DiscriminatorColumn(name = "book_extra_type")
@Data
@NoArgsConstructor
@AllArgsConstructor
public class BookExtra {
  @Id
  @GeneratedValue(strategy = GenerationType.IDENTITY)
  @Basic(optional = false)
  @Column(name = "id", nullable = false)
  protected Long id;

  @JoinColumn(name = "book_id", referencedColumnName = "id")
  @ManyToOne
  protected Book book;
  ...
}

@Entity    
@Table(name = "book_cd")
@PrimaryKeyJoinColumn(name = "id")
@DiscriminatorValue("CD")
@Data
public class BookCd extends BookExtra {
  @Column(name = "singer", length = 100)
  private String singer;
}

保存数据后，一切都很好，我将所有三个表都填满，book_extras和book_cd表中的id相等，book_extra_type设置为CD。当我想从Book实体访问CD的收藏集时出现问题：

Book b = <get the book from db>;
List<BookCd> cds = b.getCds();

我收到一个错误：java.sql.SQLException: Unknown column 'cds0_.book_id' in 'field list'。似乎休眠状态正在将指向book_cd的外键指向book表，但是它们之间有book_extras表。您能帮忙告诉我如何正确地从Book类访问CD收藏吗？

从父实体访问孙子集合

0 个答案: