Many-to-Many Delete

Hibernate

Dalam relasi Many-to-Many, proses penghapusan memiliki dua skenario yang sangat berbeda. Anda harus memahami perbedaannya agar tidak terjadi kesalahan fatal seperti terhapusnya data Master (Mata Pelajaran) secara tidak sengaja.

🔥 Dua Jenis Penghapusan

1️⃣ Menghapus Hubungan Saja (Break Association)

Skenario ini digunakan jika seorang siswa berhenti mengambil suatu Mata Pelajaran. Mata Pelajarannya tetap ada di sekolah, siswanya tetap terdaftar di sekolah, hanya hubungan mereka di tabel penghubung yang dihapus.

Logika: Hapus ID dari tabel tengah (course_student), tapi jangan hapus baris di tabel student atau course.

2️⃣ Menghapus Entitas Utama (Total Delete)

Skenario ini digunakan jika seorang Siswa dikeluarkan atau sebuah Mata Pelajaran ditiadakan.

Logika: Hapus data siswa dari tabel student dan otomatis hapus semua hubungan siswa tersebut di tabel tengah (course_student).

🚀 Implementasi Delete

1️⃣ Entity `Student` (Sisi Owner)

Sisi "Owner" adalah entitas yang menentukan konfigurasi tabel penghubung menggunakan @JoinTable.

@Entity
@Table(name = "student")
public class Student {

	@Id
	@GeneratedValue(strategy = GenerationType.IDENTITY)
	private Integer id;
	
	@Column(name = "first_name")
	private String firstName;
	
	@Column(name = "last_name")
	private String lastName;
	
	@ManyToOne(cascade = {CascadeType.DETACH, CascadeType.MERGE, CascadeType.PERSIST, CascadeType.REFRESH})
	@JoinColumn(name = "class_id")
	private Classes classes;
	
	@OneToMany(
			fetch = FetchType.LAZY,
			cascade = CascadeType.ALL)
	@JoinColumn(name = "student_id") // FK yang akan dibuat di tabel 'grade'
	private List<Grade> grades = new ArrayList<>();
	
	@ManyToMany(
			fetch = FetchType.LAZY,
			cascade = {CascadeType.DETACH, CascadeType.MERGE, CascadeType.PERSIST, CascadeType.REFRESH})
	@JoinTable(
			name = "course_student",
			joinColumns = @JoinColumn(name = "student_id"),
			inverseJoinColumns = @JoinColumn(name = "course_id"))
	private Set<Course> courses = new HashSet<>();
	
	public Student() {		
	}

	public Student(String firstName, String lastName) {
		this.firstName = firstName;
		this.lastName = lastName;
	}

	public Integer getId() {
		return id;
	}

	public void setId(Integer id) {
		this.id = id;
	}

	public String getFirstName() {
		return firstName;
	}

	public void setFirstName(String firstName) {
		this.firstName = firstName;
	}

	public String getLastName() {
		return lastName;
	}

	public void setLastName(String lastName) {
		this.lastName = lastName;
	}
	
	public Classes getClasses() {
		return classes;
	}

	public void setClasses(Classes classes) {
		this.classes = classes;
	}

	public List<Grade> getGrades() {
		return grades;
	}

	public void setGrades(List<Grade> grades) {
		this.grades = grades;
	}

	public void addGrade(Grade grade) {
		if (grades == null) {
			grades = new ArrayList<>();
		}
		
		grades.add(grade);
	}
	
	public Set<Course> getCourses() {
		return courses;
	}

	public void setCourses(Set<Course> courses) {
		this.courses = courses;
	}
	
	public void addCourse(Course course) {
		if (course == null) return;
		
		if (courses == null) {
			courses = new HashSet<>();
		}
		
		if (!courses.contains(course)) {
			courses.add(course);
			course.addStudent(this);
		}
	}

	@Override
	public String toString() {
		return "Student [id=" + id + ", firstName=" + firstName + ", lastName=" + lastName + "]";
	}
}

2️⃣ Entity `Course` (Sisi Inverse)

Sisi ini menggunakan atribut mappedBy yang merujuk pada nama variabel di class Student.

@Entity
@Table(name = "course")
public class Course {

	@Id
	@GeneratedValue(strategy = GenerationType.IDENTITY)
	private Integer id;
	
	@Column(name = "course_name")
	private String courseName;
	
	@ManyToMany(
			mappedBy = "courses",
			fetch = FetchType.LAZY,
			cascade = {CascadeType.DETACH, CascadeType.MERGE, CascadeType.PERSIST, CascadeType.REFRESH})
	private Set<Student> students = new HashSet<>();
	
	public Course() { }
	
	public Course(String courseName) {
		this.courseName = courseName;
	}

	public Integer getId() {
		return id;
	}

	public void setId(Integer id) {
		this.id = id;
	}

	public String getCourseName() {
		return courseName;
	}

	public void setCourseName(String courseName) {
		this.courseName = courseName;
	}
	
	public Set<Student> getStudents() {
		return students;
	}

	public void setStudents(Set<Student> students) {
		this.students = students;
	}

	public void addStudent(Student student) {
		if (student == null) return;
		
		if (students == null) {
			students = new HashSet<>();
		}
		
		if (!students.contains(student)) {
			students.add(student);
			student.addCourse(this);
		}
	}

	@Override
	public String toString() {
		return "Course [id=" + id + ", courseName=" + courseName + "]";
	}
}

🛢 Implementasi DAO

Membuat Interface DAO:

public interface SchoolDAO {
	
	void deleteStudentById(Integer id);

	void deleteCourseById(Integer id);
	
}

Implementasi DAO delete:

@Repository
public class SchoolDAOImpl implements SchoolDAO {

	private EntityManager entityManager;
	
	public SchoolDAOImpl(EntityManager entityManager) {
		this.entityManager = entityManager;
	}

	@Override
	@Transactional
	public void deleteStudentById(Integer id) {
		entityManager.remove(entityManager.find(Student.class, id));	
	}

	@Override
	@Transactional
	public void deleteCourseById(Integer id) {
		Course course = entityManager.find(Course.class, id);
		
		if (course != null) {
			// get a student
			Set<Student> students = course.getStudents();
			
			// break association
			for (Student student : students) {
				student.getCourses().remove(course);
			}
		
			entityManager.remove(course);
		}
	}
}

info

Khusus untuk menghapus entitas Course Dalam relasi Many-to-Many secara bersih (tanpa meninggalkan data sampah atau menyebabkan error constraint), di dalam DAO sebagai berikut penjelasan langkah demi langkahnya:

1. `@Transactional`

Anotasi ini memastikan seluruh proses di dalam metode ini berada dalam satu transaksi database. Jika salah satu langkah gagal, seluruh perubahan akan dibatalkan (rollback). Ini sangat penting karena kita melakukan perubahan pada beberapa tabel sekaligus (course dan tabel penghubung course_student).

2. `entityManager.find(Course.class, id)`

Mencari data Course berdasarkan ID di database. Objek yang ditemukan akan berstatus Persistent/Managed (terkelola oleh Hibernate).

3. `course.getStudents()`

Mengambil koleksi siswa yang mengambil kursus tersebut. Karena relasinya Many-to-Many, data ini biasanya diambil dari tabel penghubung (junction table) seperti course_student.

4. Break Association (Memutus Relasi)

for (Student student : students) {
    student.getCourses().remove(course);
}

Ini adalah bagian paling krusial dalam relasi Bi-directional Many-to-Many.

Masalah: Jika Anda langsung menghapus course, Hibernate mungkin akan error karena data course tersebut masih direferensikan oleh objek Student di memori Java atau di tabel penghubung.
Solusi: Anda harus melakukan iterasi ke setiap siswa yang mengambil kursus tersebut, lalu menghapus kursus itu dari daftar kursus (Set<Course>) milik masing-masing siswa. Ini secara otomatis akan menghapus baris terkait di tabel penghubung (course_student) saat transaksi selesai.

5. `entityManager.remove(course)`

Setelah hubungan dengan semua siswa diputus, barulah objek course itu sendiri aman untuk dihapus dari tabel course di database.

❓Kenapa harus ada loop "Break Association"?

Dalam relasi Many-to-Many yang menggunakan mappedBy (sisi Inverse), sisi Course bukanlah "pemilik" sah dari tabel penghubung. Pemiliknya adalah sisi Student.

Jika Anda menghapus Course tanpa memutus hubungan dari sisi Student, database akan menolak penghapusan karena adanya Foreign Key Constraint Violation (ada data di tabel penghubung yang masih menunjuk ke ID kursus tersebut).

✍️ Implementasi ini sangat standar untuk aplikasi berbasis Hibernate atau Spring Boot agar integritas data tetap terjaga.

▶️ Main Class

Kita akan menghapus dari sisi Course dan sisi Student.

@SpringBootApplication
public class Application {

	public static void main(String[] args) {
		SpringApplication.run(Application.class, args);
	}

	// Bean ini akan dieksekusi di command line
	@Bean
	public CommandLineRunner commandLineRunner(SchoolDAO dao) {
		return runner -> {

			deleteStudent(dao);
			
			deleteCourse(dao);
			
		};
	}

	private void deleteCourse(SchoolDAO dao) {
		int id = 3;
		dao.deleteCourseById(id);
	}

	private void deleteStudent(SchoolDAO dao) {
		int id = 4;
		dao.deleteStudentById(id);		
	}


}

Output pada Hibernate:

Hibernate: select s1_0.id,c1_0.id,c1_0.class_name,t1_0.id,t1_0.first_name,t1_0.last_name,s1_0.first_name,s1_0.last_name from student s1_0 left join classes c1_0 on c1_0.id=s1_0.class_id left join teacher t1_0 on t1_0.id=c1_0.teacher_id where s1_0.id=?
Hibernate: select g1_0.student_id,g1_0.id,g1_0.score,g1_0.subject_name from grade g1_0 where g1_0.student_id=?
Hibernate: delete from course_student where student_id=?
Hibernate: delete from student where id=?
Hibernate: select c1_0.id,c1_0.course_name from course c1_0 where c1_0.id=?
Hibernate: select s1_0.course_id,s1_1.id,c1_0.id,c1_0.class_name,t1_0.id,t1_0.first_name,t1_0.last_name,s1_1.first_name,s1_1.last_name from course_student s1_0 join student s1_1 on s1_1.id=s1_0.student_id left join classes c1_0 on c1_0.id=s1_1.class_id left join teacher t1_0 on t1_0.id=c1_0.teacher_id where s1_0.course_id=?
Hibernate: select c1_0.student_id,c1_1.id,c1_1.course_name from course_student c1_0 join course c1_1 on c1_1.id=c1_0.course_id where c1_0.student_id=?
Hibernate: select c1_0.student_id,c1_1.id,c1_1.course_name from course_student c1_0 join course c1_1 on c1_1.id=c1_0.course_id where c1_0.student_id=?
Hibernate: select c1_0.student_id,c1_1.id,c1_1.course_name from course_student c1_0 join course c1_1 on c1_1.id=c1_0.course_id where c1_0.student_id=?
Hibernate: delete from course_student where student_id=? and course_id=?
Hibernate: delete from course_student where student_id=?
Hibernate: delete from course_student where student_id=?
Hibernate: delete from course where id=?

info

Source Code: https://github.com/TimposuLabs/belajar-springboot-jpa-hibernate-advance/tree/main/16-hibernate-many-to-many-delete

🔥 Dua Jenis Penghapusan​

1️⃣ Menghapus Hubungan Saja (Break Association)​

2️⃣ Menghapus Entitas Utama (Total Delete)​

🚀 Implementasi Delete​

1️⃣ Entity Student (Sisi Owner)​

2️⃣ Entity Course (Sisi Inverse)​

🛢 Implementasi DAO​

1. @Transactional​

2. entityManager.find(Course.class, id)​

3. course.getStudents()​

4. Break Association (Memutus Relasi)​

5. entityManager.remove(course)​

❓Kenapa harus ada loop "Break Association"?​

▶️ Main Class​