Delete Values from Join Table spring boot

Question

I have two tables students and subjects. A student can have more than one subject and vice versa. I have two model classes and vave joined using Many to Many relationship in spring boot and JPA.My problem is how I can delete values from my join table. But I can't figure out how I can do delete from join table. For Student and Subject Model I delete comfortably using deleteById() function.This is my code:

          @ManyToMany
          @JoinTable(
          name = "student_subject", 
          joinColumns = @JoinColumn(name = "student_id"), 
          inverseJoinColumns = @JoinColumn(name = "subject_id"))
          private Set<SubjectModel> subjects;

//and my repository Class

          @Repository
          public interface SubjectDao extends JpaRepository<SubjectModel, Integer> {}

gal_boti12 · Accepted Answer · 2019-12-04 10:08:46Z

1

You have to delete the corresponding objects form both sides of the link, and then save them.

myStudent.getSubjects().remove(mySubject);
mySubject.getStudents().remove(myStudent);
SubjectDao subjectDao = new SubjectDao();
subjectDao.save(mySubject);

Here another examle: Hibernate: delete many-to-many association

answered Dec 4, 2019 at 10:08

gal_boti12

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Hemin · Accepted Answer · 2019-12-04 10:36:53Z

0

You have two table Student and Subject. And I suppose you want is delete one of the subject from a student. For that you should let jpa delete the row from subject and student-subject association table. And dont need to user SubjectRepository. Take a look.

Student firstStudent=studentRepository.findById(1);
Set<SubjectModel> subs=firstStudent.getSubject();
subs.clear();
firstStudent.setSubject(subs);

studentRepository.save(firstStudent);  // this method will delete the row from assiciation table as well as the subject table.

answered Dec 4, 2019 at 10:36

Hemin

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