与特定级联类型的JPA多对多关系

Question

对于我的任务，我需要使用JPA创建多对多的关系，但是连接表是手动指定的，并带有额外的列。数据结构如下所示：

• 图书（id、名称、已出版、流派、评级）
• 作者（身份证、姓名、性别、出生）
• 图书-作者（id,book-id,author-id)

我创建了这样的实体：

作者：

@Getter
@Setter
@NoArgsConstructor
@Entity
@Table(name = "authors")
public class Author {

  @Id
  @GeneratedValue(strategy = GenerationType.AUTO)
  private Long id;

  @Column(name = "name", length = 60)
  private String name;

  @Enumerated(EnumType.STRING)
  private Gender gender;

  private Date born;

  @OneToMany(mappedBy = "author",cascade = CascadeType.ALL, orphanRemoval = 
     true, fetch = FetchType.EAGER)
  private Set<AuthorBook> authorBooks = new HashSet<>();

}

书：

@Getter
@Setter
@NoArgsConstructor
@Entity
@Table(name = "books")
public class Book {

  @Id
  @GeneratedValue(strategy = GenerationType.AUTO)
  private Long id;

  private String name;

  private Date published;

  private String genre;

  private BigDecimal rating;

  @OneToMany(mappedBy = "book",cascade = CascadeType.REMOVE, fetch = 
    FetchType.EAGER)
  @OnDelete(action = OnDeleteAction.CASCADE)
  private Set<AuthorBook> authorBooks = new HashSet<>();

}

@Data
@EqualsAndHashCode(exclude = {"book", "author"})
@Entity
@Table(name = "author_book")
public class AuthorBook implements Serializable {

  @Id
  @GeneratedValue(strategy = GenerationType.AUTO)
  private Long id;

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

  @ManyToOne(cascade = CascadeType.ALL)
  @JoinColumn(name = "author_id")
  private Author author;
}

 id       name              published       genre               rating
 1     'Залишенець'         '2005-02-03'    'historical novel'  '5'
 2     'Ключ'               '1999-01-01'    'novel'             '3'
 3     'Effective Java'     '2001-03-02'    'technical'         '5'
 4     'Java Concurrency'   '2006-04-23'    'technical'         '4'
 5     'Java Puzzlers'      '2005-02-02'    'technical'         '4'
 6     'Patterns'           '2002-06-25'    'technical'         '3'
 7     'Harry Potter'       '1997-06-26'    'fantasy'           '5'
 8     'The Programmer'     '1999-09-21'    'education'         '5'
 9     'The Lost Symbol'     null           'crime'             '4'

id            name                  gender       born    
1      'Шкляр Василь Миколайович'   'male'      '1951-06-10'
2      'Joshua Bloch'               'male'      '1961-07-28'
3      'Martin Fowler'              'male'       null
4      'Chad Fowler'                'male'       null
5      'J. K. Rowling'              'female'    '1965-07-31'
6      'Dan Brown'                  'male'      '1964-06-22'
7      'Suzanne Collins'            'female'    '1962-08-10'

AuthorBook表：

id   book_id   author_id
 1    1       1
 2    2       1
 3    3       2
 4    4       2
 5    5       2
 6    6       3
 7    9       6
 8    8       4
 9    7       5

例如，当我删除ID=2的book，它将删除ID=1的author。有没有什么方法可以在不删除已绑定作者的同时删除书籍。与author表相同的是：删除author时，我不应该删除他的书。我是Spring Data JPA的新手，如果这个问题是愚蠢的，那么很抱歉。

更新

public class AuthorBook implements Serializable {

  @Id
  @GeneratedValue(strategy = GenerationType.IDENTITY)
  private Long id;

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

  @ManyToOne
  @JoinColumn(name = "author_id")
  private Author author;
}

Book和Author实体保持不变。现在，当我尝试使用JPA的deleteById（idValue）删除id=1的book，它抛出

javax.persistence.EntityNotFoundException: Unable to find Book with id 1

它实际上从books表中删除了book，但没有从AuthorBook表中删除关联的记录，我的意思是books表中没有ID=1的book，但AuthorBook表中仍然有记录：

id   book_id   author_id
1     1         1 

ID=1的图书记录删除后的MySql截图

图书表：在此输入图像说明

作者表：在此输入图像描述

Answer 1

您正在强制实体删除具有此标记(cascade=cascadeType.all)的从属记录

CascadeType.all的含义是持久性将所有EntityManager操作（PERSIST、REMOVE、REFRESH、MERGE、DETACH）传播（级联）到相关实体。

如果您不想删除依赖记录，请从实体中删除此标记，这可能会导致在表中留下孤立记录（不是一个好的做法）。