Persisting pojo with collection attribute using Hibernate

[Kristofer Hindersson]

Hi, I'm having difficulties understanding how to persist a bean/pojo/class with a collection holding another pojo. How should I go about solving the following example:

I have these two entities:

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

	private Integer id;
	private String name;
	private List<Book> bibliography;

	@Id
	@GeneratedValue(strategy=GenerationType.AUTO)
	public Integer getId() {
		return this.id;
	}

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

	public String getName() {
		return this.name;
	}

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

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

	public void setBibliography(List<Book> bibliography) {
		this.bibliography = bibliography;
	}
}

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

	private Integer id;
	private String title;
	private Author author;

	@Id
	@GeneratedValue(strategy=GenerationType.AUTO)
	public Integer getId() {
		return this.id;
	}

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

	public String getTitle() {
		return this.title;
	}

	public void setTitle(String title) {
		this.title = title;
	}
	
	@ManyToOne
	@JoinColumn(name="author_id")
	public Author getAuthor() {
		return this.author;
	}

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

and I've created a database with these tables:

CREATE TABLE books (
	id INTEGER PRIMARY KEY AUTO_INCREMENT,
	title VARCHAR(255),
	author_id INTEGER REFERENCES authors
);

CREATE TABLE authors (
	id INTEGER PRIMARY KEY AUTO_INCREMENT,
	name VARCHAR(255)
);

Now let's say that I already have an author with a populated bibliography and I want to persist this to the database.

What I already tried was using hibernates merge by calling this method:

public void save(Author author) throws DataAccessException {
    sessionFactory.getCurrentSession().merge(author);
}

Like this

...service.save(author)

Unfortunately this doesn't seem to work as the foreign key author_id in books is never set (NULL).

What should I be doing different?