Spring JPA-删除One-toMany关系中的子级

Question

我有以下作者类：

@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;
    }
 }

@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;
    }

}

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

@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，它就会自动添加到图书存储库中。但是如果我从存储库中移除一本书，我如何从作者那里移除它呢？

Answer 1

好吧，对不起，我没有仔细看你的问题。答案很简单，这次我真的尝试了。您需要从POJO中的父级中删除子级，并在没有子级的情况下重新保存父级。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（应该如此），只需从author POJO中删除这本书，保存author时，cascade=cascadeType.all将为您传播删除这本书。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);