如何在Spring MVC中提交ManyToMany属性

Question

@Entity
@Table(name = "book")
public class Book {

    @Id
    @GeneratedValue()
    private Long id;

    private String title;

    @ManyToMany
    @JoinTable(name = "book_author", joinColumns = @JoinColumn(name = "author_id", referencedColumnName = "id"), inverseJoinColumns = @JoinColumn(name = "book_id", referencedColumnName = "id"))
    private List<Author> authors;
...

@Entity
@Table(name="author")
public class Author {

    @Id
    @GeneratedValue()
    private Long id;

    private String name;

    @JsonBackReference
    @ManyToMany(mappedBy="authors")
    private List<Book> books;
...

当我自己插入SQL值时，这工作很好。

我有一个@PostMapping，它将接收编辑后的表单。

@GetMapping("/books/{bookId}/edit")
public String editBookForm(@PathVariable(value="bookId") long id, Model model){
    Book book = bookRepository.findOne(id);
    List<Author> authors = new LinkedList<>();
    for ( Author author : authorRepository.findAll())
        authors.add(author);

    model.addAttribute("book", book);
    model.addAttribute("authors", authors);
    return "bookedit";
}


@PostMapping("/books/{bookId}/edit")
public String editBookSubmit(@PathVariable(value="bookId") long id, @ModelAttribute Book book){
    bookRepository.save(book);
    return "redirect:/books/" + id;
}

这里是我的表单代码：

<form action="#" th:action="@{/books/{id}/edit(id=${book.id})}" th:object="${book}" method="post">
    <input type="hidden" th:field="*{id}" th:value="${book.id}"/>
    <div class="form-group">
        <label for="title">Book title:</label>
        <input type="text" class="form-control" id="title" th:field="*{title}" th:value="${book.title}"/>
    </div>

    <div class="form-group">
        <label for="author">Authors</label>
        <input list="author"/>

        <datalist id="author">
            <option th:each="author : ${authors}" th:value="${author.name}"></option>
        </datalist>
    </div>
    <input type="submit" class="btn btn-default" value="Save"/>
</form>