单向One To Many关联添加方法触发Proxy调用异常求助

错误信息 #

at jdk.proxy2/jdk.proxy2.$Proxy106.save(Unknown Source) ~[na:na] at
com.example.OneToManyUniDirectional.service.concretes.AuthorManager.addAuthor(AuthorManager.java:50)
~[classes/:na] at
com.example.OneToManyUniDirectional.controller.AuthorController.addAuthors(AuthorController.java:21)
~[classes/:an]

相关代码 #

Author实体类 #

public class Author {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    @Column(name="name")
    private String firstName;
    @Column(name="surname")
    private String lastName;
    @OneToMany(cascade=CascadeType.MERGE,fetch = FetchType.EAGER)
    private Set<Book> books=new HashSet<>();
    
}

Book实体类 #

public class Book {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private String isbn;
    @Column(name="book_name")
    private String name;
}

addAuthor业务方法 #

@Override
public void addAuthor(CreateAuthor createAuthor){
    Author author=new Author();
    author.setFirstName(createAuthor.getFirstName());
    author.setLastName(createAuthor.getLastName());
    if(this.bookRepository.findById(createAuthor.getBook().getId()).isPresent()){
        UpdateBook updateBook=new UpdateBook();
        updateBook.setName(createAuthor.getBook().getName());
        updateBook.setIsbn(createAuthor.getBook().getIsbn());
        this.bookService.updateBook(updateBook,createAuthor.getBook().getId());
    }
    else{
        CreateBook createBook=new CreateBook();
        createBook.setName(createAuthor.getBook().getName());
        createBook.setIsbn(createAuthor.getBook().getIsbn());
        this.bookService.addBook(createBook);
        author.getBooks().add(createAuthor.getBook());
    }
    this.authorRepository.save(author);
}

CreateAuthor DTO #

@Data
@NoArgsConstructor
@AllArgsConstructor
public class CreateAuthor {
    private String firstName;
    private String lastName;
    private Book book;
}

Controller代码 #

@PostMapping("/authors")
public void addAuthors(@RequestBody CreateAuthor createAuthor){
    this.authorService.addAuthor(createAuthor);
}

注：CreateBook和UpdateBook类不含id属性

报错原因分析 #

1. 单向OneToMany关联配置缺失：@OneToMany未指定@JoinColumn，Hibernate会自动创建中间表维护关联，但此时关联的Book实体状态不符合要求，导致保存Author时关联处理失败。
2. 游离态实体操作问题：CreateAuthor中传递的Book是从请求体反序列化的游离态对象，cascade=CascadeType.MERGE仅支持合并持久态或托管态实体，无法处理游离态，触发代理类的save方法报错。
3. 新增Book后关联对象错误：新增Book时，调用bookService.addBook(createBook)后，直接将传入的未持久化Book对象添加到Author的集合，该对象未被Hibernate托管，保存Author时无法正确关联。

解决办法 #

1. 修正OneToMany关联配置 #

给Author的@OneToMany添加@JoinColumn，明确外键列，避免自动生成中间表，同时调整cascade类型覆盖新增场景：

@OneToMany(cascade = {CascadeType.MERGE, CascadeType.PERSIST}, fetch = FetchType.EAGER)
@JoinColumn(name = "author_id") // 指定Book表中的外键列
private Set<Book> books = new HashSet<>();

2. 重构CreateAuthor的字段类型 #

不要直接传递Book实体，改用CreateBook DTO，避免传递游离态实体：

@Data
@NoArgsConstructor
@AllArgsConstructor
public class CreateAuthor {
    private String firstName;
    private String lastName;
    private CreateBook book; // 替换为CreateBook DTO
}

3. 修正addAuthor方法逻辑 #

确保添加到Author集合的是持久态Book对象，同时简化逻辑：

@Override
public void addAuthor(CreateAuthor createAuthor){
    Author author = new Author();
    author.setFirstName(createAuthor.getFirstName());
    author.setLastName(createAuthor.getLastName());
    
    CreateBook createBook = createAuthor.getBook();
    Book book;
    // 检查Book是否存在（需给CreateBook添加id字段支持更新场景）
    if (createBook.getId() != null && bookRepository.findById(createBook.getId()).isPresent()) {
        // 更新现有Book
        book = bookRepository.findById(createBook.getId()).get();
        book.setName(createBook.getName());
        book.setIsbn(createBook.getIsbn());
        bookRepository.save(book);
    } else {
        // 新增Book并获取持久态对象
        book = new Book();
        book.setName(createBook.getName());
        book.setIsbn(createBook.getIsbn());
        book = bookRepository.save(book);
    }
    // 将持久态Book添加到Author集合
    author.getBooks().add(book);
    authorRepository.save(author);
}

4. 调整BookService的addBook方法 #

确保addBook返回持久化后的Book对象：

public Book addBook(CreateBook createBook) {
    Book book = new Book();
    book.setName(createBook.getName());
    book.setIsbn(createBook.getIsbn());
    return bookRepository.save(book);
}

内容的提问来源于stack exchange，提问作者samaritan