Grails addTo *方法不保存1：M关系中的子对象

Question

我有一些Java类，我正在与Grails（2.4.0）项目集成（我需要使用Java类，因为我们应用程序中的其他项目都是纯Java）。当我创建父对象并添加子对象然后保存时，MySQL返回一个错误，指出外键字段不能为空。看来父母的主键没有插入到孩子的外键字段中。

我是否缺少JPA选项来启用级联保存/插入？

Groovy代码

def author = new Author(name:"Joe")
    .addToBooks(
        new Book(title:"My Title")
    )
    .save(failOnError:true)

错误

Message: Hibernate operation: could not execute statement; SQL [n/a]; NULL not allowed for column "AUTHOR_ID"; SQL statement:
insert into book (id, author_id, title) values (null, ?, ?) [23502-173]; nested exception is org.h2.jdbc.JdbcSQLException: NULL not allowed for column "AUTHOR_ID"; SQL statement:
insert into book (id, author_id, title) values (null, ?, ?) [23502-173]

Author.java

@Entity
public class Author {
    private long id;
    private List<Book> books;
    private String name;

    @Id
    @Column
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    public long getId() {
        return id;
    }

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

    @OneToMany(cascade = CascadeType.ALL, mappedBy = "author")
    public List<Book> getBooks() {
        return books;
    }

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

    @Column
    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

}

Book.java

@Entity
public class Book {
    private int id;
    private String title;
    private Author author;

    @Id
    @Column
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    public int getId() {
        return id;
    }

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

    @Column(name="TITLE")
    public String getTitle() {
        return title;
    }

    public void setTitle(String title) {
        this.title = title;
    }

    @ManyToOne(fetch = FetchType.LAZY, optional = false)
    @JoinColumn(name = "AUTHOR_ID", foreignKey = @ForeignKey(name = "author_fk1"), nullable = false)
    public Author getAuthor() {
        return author;
    }

    public void setAuthor(Author author) {
        this.author = author;
    }

}