Spring JPA - 删除一对多关系中的子级

Question

我有以下 Author 类：

@Entity
public class Author  implements Serializable{

    private static final long serialVersionUID = 1L;

    @Id
    @GeneratedValue
    private Long id;

    @OneToMany(fetch = FetchType.EAGER, cascade=CascadeType.ALL)
    @JoinTable(
        name="author_book",
        joinColumns = @JoinColumn( name="author_id"),
        inverseJoinColumns = @JoinColumn( name="book_id")
    )
    private Set<Book> books= new HashSet<Book>();

    public Author() {
        super();
    }

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public Set<Book> getBooks() {
       return books;
    }

    public void setBooks(Set<Book> books) {
        this.books = books;
    }
 }

我还有以下图书实体：

@Entity
public class Book implements Serializable{

    private static final long serialVersionUID = 1L;

    @Id
    @GeneratedValue
    private Long id;

    public Book() {
        super();
    }

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

}

接下来，我有以下两个仓库：

public interface BookRepository extends CrudRepository<Book, Long> {
}
public interface AuthorRepository extends CrudRepository<Author, Long>{
}

最后，我有以下测试用例：

@RunWith(SpringJUnit4ClassRunner.class)
@SpringApplicationConfiguration(Application.class)
public class AuthorRepositoryIntegrationTests {

    @Autowired
    AuthorRepository authorRepository;
    @Autowired
    BookRepository bookRepository;

    @Test
    @Transactional
    public void deleteBookFromAuthor() {
        Book book= new Book();
        Author author= new Author();
        author.getBooks().add(book);
        author=this.authorRepository.save(author);

        Iterable<Author> authors = this.authorRepository.findAll();
        author=authors.iterator().next();
        book=author.getBooks().iterator().next();
        this.bookRepository.delete(book);

        authors = this.authorRepository.findAll();
        assertEquals(authors.iterator().next().getBooks().size(),0);
    }
}

我的问题是这个测试用例中的最后一个断言失败了。如果我向作者添加一本书，它会自动添加到图书存储库中。但是，如果我从存储库中删除一本书，我如何从作者那里删除它？

Answer 1

REDO：好的，抱歉，我没有仔细看你的问题。答案虽然很简单，但这次我真的试过了。您需要从 POJO 中的父级中删除子级并重新保存没有子级的父级。请参阅下面的注释代码：

List<Book> books = new ArrayList<Book>();

Book book = new Book();
books.add(book);

Author author = new Author();
author.setBooks(books);
authorRepository.save(author);

Author a =authorRepository.findAll().iterator().next();
Book b = a.getBooks().get(0);
bookRepository.delete(b);

// REMOVE FROM PARENT
a.getBooks().remove(0);
authorRepository.save(a);

a = authorRepository.findAll().iterator().next();
System.out.println(a);

编辑：如果您担心一致性，您应该这样做，只需从作者 POJO 中删除该书，当您保存作者时，cascade=CascadeType.ALL 将为您传播删除该书。例如：

Author a =authorRepository.findAll().iterator().next();
a.getBooks().remove(0);
authorRepository.save(a);

// NO BOOK
a = authorRepository.findAll().iterator().next();
System.out.println(a);