detached entity passed to persist error while using #ManyToOne association - spring

Question

I have Book & Bookdetail class
When I am trying to use same BookDetail information for my two Book objects using #ManyToOne, I am getting
"detached entity passed to persist error".
I tried same with JpaRepository and CrudRepository. But same result
Please help me. Thanks in advance
Main Class
#SpringBootApplication
public class HelloJpaApplication implements CommandLineRunner{
private static final Logger logger = LoggerFactory.getLogger(HelloJpaApplication.class);
#Autowired
private BookRepository bookRepository;
public void run(String... arg0) throws Exception {
Book book1=new Book();
book1.setName("my thoughts");
Book book2=new Book();
book2.setName("your thoughts");
Bookdetail detail=new Bookdetail();
detail.setCategory("good books");
book1.setBookdetail(detail);
book2.setBookdetail(detail);
bookRepository.save(book1);
bookRepository.save(book2);
}
public static void main(String[] args) {
SpringApplication.run(HelloJpaApplication.class, args);
}
}
BookRepository interface
public interface BookRepository extends JpaRepository<Book,Integer>{
}
Book class
#Entity
public class Book {
#Id
#GeneratedValue(strategy=GenerationType.AUTO)
private int bookid;
private String name;
#ManyToOne(cascade = {CascadeType.PERSIST,CascadeType.MERGE})
private Bookdetail bookdetail;
public Book() {
}
public Book(String name) {
this.name=name;
}
public int getBookid() {
return bookid;
}
public void setBookid(int bookid) {
this.bookid = bookid;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public Bookdetail getBookdetail() {
return bookdetail;
}
public void setBookdetail(Bookdetail bookdetail) {
this.bookdetail = bookdetail;
}
}
Bookdetail Class
#Entity
#Table(name="bookdetail")
public class Bookdetail {
#Id
#GeneratedValue(strategy=GenerationType.AUTO)
private int bookid;
private String category;
public Bookdetail() {
}
public Bookdetail(String category) {
this.category=category;
}
public String getCategory() {
return category;
}
public void setCategory(String category) {
this.category = category;
}
}

Answer 1

Every object created just with Bookdetail detail=new Bookdetail(); is a detached entity which mean he's not in the hibernate session or don't have a identifier id.
And you have to wrap your services which persist or update or delete into a transaction.
So first you must save detail your detached entity : bookdetailRepository.save(detail) to attached it to the session But in your case you already specify cascade = {CascadeType.PERSIST,CascadeType.MERGE}
#ManyToOne(cascade = {CascadeType.PERSIST,CascadeType.MERGE})
private Bookdetail bookdetail;
No need to save it before, the job will be done automatically.
the solution then is to annotate the method run() with #Transactional
...
#Transactional
public void run(String... arg0)
...
bookdetailRepository.save(detail)
book1.setBookdetail(detail);
...

Answer 2

#Transactional before public void run() worked for me... Thank you very much #Youssef and #Chathuranga Tennakoon for your efforts. Sharing the code for others.
#SpringBootApplication
// #EnableJpaRepositories(basePackages = {"com.jpa.repository"})
public class HelloJpaApplication implements CommandLineRunner {
private static final Logger logger = LoggerFactory.getLogger(HelloJpaApplication.class);
#Autowired
private BookRepository bookRepository;
// #Autowired
// private BookDetailRepository bookDetailRepository;
#Transactional
public void run(String... arg0) throws Exception {
Book book1 = new Book();
book1.setName("my thoughts");
Book book2 = new Book();
book2.setName("your thoughts");
Bookdetail detail = new Bookdetail();
detail.setCategory("good books");
// bookDetailRepository.save(detail);
book1.setBookdetail(detail);
book2.setBookdetail(detail);
bookRepository.save(book1);
bookRepository.save(book2);
}
public static void main(String[] args) {
SpringApplication.run(HelloJpaApplication.class, args);
}
}
#Entity
public class Book {
#Id
#GeneratedValue(strategy = GenerationType.AUTO)
private int bookid;
private String name;
#ManyToOne(cascade = CascadeType.ALL)
private Bookdetail bookdetail;
public Book() {
}
public Book(String name) {
this.name = name;
}
public int getBookid() {
return bookid;
}
public void setBookid(int bookid) {
this.bookid = bookid;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public Bookdetail getBookdetail() {
return bookdetail;
}
public void setBookdetail(Bookdetail bookdetail) {
this.bookdetail = bookdetail;
}
}
#Entity
#Table(name = "bookdetail")
public class Bookdetail {
#Id
#GeneratedValue(strategy = GenerationType.AUTO)
private int bookid;
private String category;
public Bookdetail() {
}
public Bookdetail(String category) {
this.category = category;
}
public String getCategory() {
return category;
}
public void setCategory(String category) {
this.category = category;
}
}
#Repository
public interface BookRepository extends JpaRepository<Book,Integer>{
}

Answer 3

Add BookdetailRepository as follows.
#Repository
public interface BookdetailRepository extends JpaRepository<Bookdetail,Integer> {
}
And change the HelloJpaApplication as follows.
#SpringBootApplication
#EnableJpaRepositories(basePackages = {"com.jpa"})
public class HelloJpaApplication implements CommandLineRunner{
private static final Logger logger = LoggerFactory.getLogger(HelloJpaApplication.class);
#Autowired
private BookRepository bookRepository;
#Autowired
BookdetailRepository bookdetailRepository;
public void run(String... arg0) throws Exception {
Book book1=new Book();
book1.setName("my thoughts");
Book book2=new Book();
book2.setName("your thoughts");
Bookdetail detail=new Bookdetail();
detail.setCategory("good books");
bookdetailRepository.save(detail); //saving the bookDetail
book1.setBookdetail(detail);
book2.setBookdetail(detail);
bookRepository.save(book1);
bookRepository.save(book2);
}
public static void main(String[] args) {
SpringApplication.run(HelloJpaApplication.class, args);
}
}