hibernate CompositeKey

hibernate CompositeKey

https://www.baeldung.com/hibernate-many-to-many

https://www.baeldung.com/jpa-many-to-many

https://thorben-janssen.com/hibernate-tip-many-to-many-association-with-additional-attributes/

Many to many with addtional attributes

Screen Shot 2020-11-26 at 11.20.18 PM

JoinTable 无法添加新属性

You need to model the book_publisher table as an entity with 2 many-to-one relationships to the Book and Publisher entities.

@Entity
class BookPublisher {
 
    @EmbeddedId
    private BookPublisherId id = new BookPublisherId();
 
    @ManyToOne
    @MapsId("bookId")
    private Book book;
 
    @ManyToOne
    @MapsId("publisherId")
    private Publisher publisher;
 
    private Format format;
     
    ...
}

@Embeddable
public static class BookPublisherId implements Serializable {
 
    private static final long serialVersionUID = 1L;
 
    private Long bookId;
    private Long publisherId;
 
    public BookPublisherId() {
 
    }
 
    public BookPublisherId(Long bookId, Long publisherId) {
        super();
        this.bookId = bookId;
        this.publisherId = publisherId;
    }
 
    public Long getBookId() {
        return bookId;
    }
 
    public void setBookId(Long bookId) {
        this.bookId = bookId;
    }
 
    public Long getPublisherId() {
        return publisherId;
    }
 
    public void setPublisherId(Long publisherId) {
        this.publisherId = publisherId;
    }
 
    @Override
    public int hashCode() {
        final int prime = 31;
        int result = 1;
        result = prime * result
                + ((bookId == null) ? 0 : bookId.hashCode());
        result = prime * result
                + ((publisherId == null) ? 0 : publisherId.hashCode());
        return result;
    }
 
    @Override
    public boolean equals(Object obj) {
        if (this == obj)
            return true;
        if (obj == null)
            return false;
        if (getClass() != obj.getClass())
            return false;
        BookPublisherId other = (BookPublisherId) obj;
        return Objects.equals(getBookId(), other.getBookId()) && Objects.equals(getPublisherId(), other.getPublisherId());
    }
}

Mapping as a Bidirectional Association

@Entity
public class Book {
 
    @Id
    @GeneratedValue
    private Long id;
 
    @OneToMany(mappedBy = "publisher")
    private Set<BookPublisher> bookPublishers = new HashSet<>();
     
    ...
}

@Entity
public class Publisher {
 
    @Id
    @GeneratedValue
    private Long id;
 
    @OneToMany(mappedBy = "publisher")
    private Set<BookPublisher> bookPublishers = new HashSet<>();
     
    ...
}

Using the Mapping

Book b = new Book();
b.setTitle("Hibernate Tips - More than 70 solutions to common Hibernate problems");
em.persist(b);
 
Publisher p = new Publisher();
p.setName("Thorben Janssen");
em.persist(p);
 
BookPublisher bp = new BookPublisher();
bp.setBook(b);
bp.setPublisher(p);
p.getBookPublishers().add(bp);
b.getBookPublishers().add(bp);