JPA @ManyToMany 关系

Question

I have a case with Many to Many relationship

Following is the Book class with isbn as unique identifier

 @Entity @Table(name = "book") public class Book implements Serializable { private static final long serialVersionUID = -4643154384069203197L; @Id @Column(name = "id") @GeneratedValue(strategy = GenerationType.IDENTITY) private long id; @Column(name = "isbn") private String isbn; @ManyToMany(cascade = CascadeType.ALL) @JoinTable(name = "book_author", joinColumns = { @JoinColumn(name = "bookId", referencedColumnName = "id") }, inverseJoinColumns = { @JoinColumn(name = "authorId", referencedColumnName = "id") }) private Set<Author> authors = new HashSet<>(); // Getters and setters // hashcode and equals using only isbn

Following is the Author class with email as unique identifier

 @Entity @Table(name = "author") public class Author implements Serializable{ private static final long serialVersionUID = -6907306347041383886L; @Id @Column(name = "id") @GeneratedValue(strategy = GenerationType.IDENTITY) private long id; @Column(name = "email") private String email; @Column(name = "book") @ManyToMany(mappedBy = "authors") private Set<Book> books = new HashSet<>(); //getters and setters // hashcode and equals using only "email"

I am able to achieve unique Book, as the Set checks the isbn and removes all the duplicates. Since every Book can have many authors and vice versa I tried with Many to Many rekationship.

The problem comes with the unique email , Every book has an individual authors Set. How can I achevie author with unique email in the author table?

Help would be appreciated. Thanks in Advance

Answer 1

Change you @Column(name="email") into @Column(unique = true)

name="email" is redundant since by default it will grab the name of the attribute which is anyways email