CODEWITHSUNDEEP
javahibernatejpa
Ilya
Ilya

Reputation: 29703

Hibernate: insert ManyToMany, generate ID in relationship table

Let I have Tables (Books and Authors have ManyToMany relation ship)

BOOKS
id
book_name

AUTHORS
id
author_name

BOOKS_AUTHORS
id
book_id
author_id

I map this Tables on Entities 

class Books  
{  
   @Id  
   long id;  

  @Column(name = "author_name")
   String name;


   @ManyToMany(fetch = FetchType.EAGER, cascade = CascadeType.ALL)
   @JoinTable(name = "BOOKS_AUTHORS", 
              joinColumns = @JoinColumn(name = "book_id"),
              inverseJoinColumns = @JoinColumn(name = "author_id"))  
   List<Authots> authors;  

// setter, getters, adder  
}  

class Authors  
{  
   @Id  
   long id;  

   @Column(name = "author_name")
   String name;

   @ManyToMany(fetch = FetchType.EAGER, cascade = CascadeType.ALL)
   @JoinTable(name = "BOOKS_AUTHORS", 
              joinColumns = @JoinColumn(name = "author_id"),
              inverseJoinColumns = @JoinColumn(name = "book_id"))  
   List<Books> books;  

// setter, getters, adder  
}

Now, I try do next 

public void addAuthor(final String bookName, final Author author)
{  
      final Book book = // get book from database by bookName
      if (book == null)
         throw new DataNotFoundException("Book not found :(");
      author.addBook(book);
      book.addAuthor(author);  
      entityManager.persist(author);  
}

1) I get exception that ID of BOOKS_AUTHORS record must be not NULL
2) How I can Generate ID (ising sequance generator) for relationship-table BOOKS_AUTHORS

Upvotes: 5

Views: 8447

Answers (4)

Tom
Tom

Reputation: 1

In SpringBoot 1.5.3 and spring-boot-starter-data-jpa you can use annotation {@OrderColumn(name = "id")}. For you example it should looks like:

    @ManyToMany(fetch = FetchType.EAGER, cascade = CascadeType.ALL)
       @JoinTable(name = "BOOKS_AUTHORS", 
          joinColumns = @JoinColumn(name = "author_id"),
          inverseJoinColumns = @JoinColumn(name = "book_id")) 
    @OrderColumn(name = "id")             
    List<Books> books;

Upvotes: 0

Endiss
Endiss

Reputation: 699

Try using Projection

                  session.CreateCriteria(typeof (BOOKS_AUTHORS))
                           .SetProjection(Projections.Max("Id"))
                           .UniqueResult()

and add to it +1 :) Sory its .net code im not familiar with java hope it will help you.

Upvotes: 0

Bitmap
Bitmap

Reputation: 12538

@Id
@GeneratedValue(strategy=GenerationType.AUTO)
private long id;

If books_authors is not mapped using Hibernate, then use the database side auto id incrementor. Example:

ALTER table book_authors CHANGE id long NOT NULL AUTO_INCREMENT;

Upvotes: 1

axtavt
axtavt

Reputation: 242786

You cannot use @ManyToMany to create join table with id field in it.

If id field in the join table is a requirement, you have to create a special entity class (such as BookAuthor) for that table and connect it with books and authors with @ManyToOne/@OneToMany relationships.

Otherwise you need to remove id field from BOOKS_AUTHORS table.

Upvotes: 12

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