spring data jpa bidirectional mapping is not working

[iurii sherstoi]

Hi all.

Let's assume I have two entities Student and Book. One student could have many books.

Student.java

@Entity
@Table (name="Student")
class Student {
    @Id
    @Column (name="student_id")
    private int id;

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

    @OneToMany(fetch = FetchType.EAGER, mappedBy = ("student"),cascade = CascadeType.ALL)
    private Set<Book> book = new HashSet<Book>();
    // get and set methods...
}

Book.java

@Entity
@Table(name="Book")
class Book {
    @Id
    @Column (name="book_id")
    private int id;

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

    @ManyToOne(cascade=CascadeType.ALL, fetch = FetchType.LAZY)
    @JoinColumn(name="student_id", nullable = false)
    private Student student;
    // get and set methods...
}

I also have next repositories:

public interface StudentRepository extends JpaRepository<Student, Integer>{
}
public interface BookRepository extends JpaRepository<Book, Integer> {
}

My services are looking like this:

@Service
public class StudentServiceImpl implements StudentService {
    @Autowired
    private StudentRepository studentRepository;

    @Override
    public List<Student> getAllStudents() {
        return studentRepository.findAll();
    }
}

@Service
public class BookServiceImpl implements BookService {
    @Autowired
    private BookRepository bookRepository;

    @Override
    public List<Book> getAllBooks() {
        return bookRepository.findAll();
    }
}

And controller:

@Controller
public class MainController {

    private StudentService studentService;

    private BookService bookService;

    @Autowired(required = true)
    @Qualifier(value = "studentService")
    public void setStudentService(StudentService studentService) {
        this.studentService = studentService;
    }

    @Autowired(required = true)
    @Qualifier(value = "bookService")
    public void setBookService(BookService bookService) {
        this.bookService = bookService;
    }

    @RequestMapping(value="/students", method=RequestMethod.GET)
    public @ResponseBody List<Student> getStudents() {
            return studentService.getAllStudents();
    }

.................................................................

I insert few test records to DB, so when I put next url

/students

in browser, I see a lot of the same nested data:

[{"id":1,"name":"Egor","book":[{"id":2,"name":"Effective Java","student":
{"id":1,"name":"Egor","book":[{"id":2,"name":"Effective Java","student":
{"id":1,"name":"Egor","book":[{"id":2,"name":"Effective Java","student":
{"id":1,"name":"Egor","book":[{"id":2,"name":"Effective Java","student":
......................................................................

What is wrong with my mapping?

Thanks in advance.

[Roel De Nijs]

Hi iurii sherstoi,

First of all, a warm welcome to CodeRanch!

iurii sherstoi wrote:What is wrong with my mapping?

Let's start with the beginning: is the data in the database tables Student and Book correct? Meaning: do you have different records (with a different primary key) and are relationships between records valid (using correct foreign keys)?

Kind regards,
Roel

[iurii sherstoi]

Hi Roel,

Thanks for replay and sorry for delay. Yes, table structure looks correct for me.
Student table:

STUDENT_ID	STUDENT_NAME
1	Misha
2	Egor

I have next key for Student table:
CONSTRAINT student_pk PRIMARY KEY (student_id)

[iurii sherstoi]

Sorry have some issue with html table tag for my post (can't insert two html tables in one post).
So here is continue.

Book table:

BOOK_ID	BOOK_NAME	STUDENT_ID
1	Thinking in Java	1
2	Effective Java	1
3	Effective SQL	2

So I have next keys for Book table.
CONSTRAINT book_pk PRIMARY KEY (book_id), CONSTRAINT student_fk FOREIGN KEY (student_id) REFERENCES student (student_id)
So as for me mapping looks fine but still don't understand why do I see nested data...

[Roel De Nijs]

That's odd! Everything seems ok to me and your mapping looks almost similar to the example in the Java Persistence wikibook.

So you'll have some debugging to do If you are using at least JPA 2.0, I would try the unidirectional OneToMany without the inverse ManyToOne and verify if this gets you the expected/desired list of students.