One-to-Many Create
Pada materi sebelumnya kita sudah memiliki Entity:
1️⃣ Entity Student (Sisi "Many" / Owner)
Sisi ini yang memegang @JoinColumn.
@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;
// Setter & Getter
}
2️⃣ Entity Classes (Sisi "One" / Inverse)
Sisi ini menggunakan mappedBy dan memiliki koleksi (List atau Set).
@Entity
@Table(name = "classes")
public class Classes {
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private Integer id;
@Column(name = "class_name")
private String className;
@OneToOne(cascade = {CascadeType.DETACH, CascadeType.MERGE, CascadeType.PERSIST, CascadeType.REFRESH})
@JoinColumn(name = "teacher_id")
private Teacher teacher;
@OneToMany(mappedBy = "classes", cascade = {CascadeType.DETACH, CascadeType.MERGE, CascadeType.PERSIST, CascadeType.REFRESH})
List<Student> students = new ArrayList<>();
// HELPER METHOD: Sangat penting untuk sinkronisasi 2 arah di memori
// menambah method 'add()' memastikan kedua sisi terhubung secara konsisten dalam memori Java dengan Bi-Direction
public void add(Student student) {
if (students == null) {
students = new ArrayList<>();
}
students.add(student);
if (student != null) {
student.setClasses(this);
}
}
// Setter & Getter
}
3️⃣ Main Class
- Pada main class application kita akan membuat
Classesdengan berisi dataStudent:
@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 -> {
createClassWithStudent(dao);
};
}
private void createClassWithStudent(SchoolDAO dao) {
Teacher teacher = new Teacher("Hatake", "Kakashi");
Classes class10 = new Classes("Kelas 10", teacher);
Student naruto = new Student("Uzumaki", "Naruto");
Student sasuke = new Student("Uciha", "Sazuke");
Student sakura = new Student("Haruno", "Sakura");
class10.add(naruto);
class10.add(sasuke);
class10.add(sakura);
dao.saveClasses(class10);
System.out.println("Saved classes: " + class10);
System.out.println("List student: " + class10.getStudents());
}
}
- Output pada Hibernate SQL:
Hibernate: insert into teacher (first_name,last_name) values (?,?)
Hibernate: insert into classes (class_name,teacher_id) values (?,?)
Hibernate: insert into student (class_id,first_name,last_name) values (?,?,?)
Hibernate: insert into student (class_id,first_name,last_name) values (?,?,?)
Hibernate: insert into student (class_id,first_name,last_name) values (?,?,?)
Saved classes: Class [id=4, className=Kelas 10, teacher=Guru [id=4, firstName=Hatake, lastName=Kakashi]]
List student: [Student [id=7, firstName=Uzumaki, lastName=Naruto], Student [id=8, firstName=Uciha, lastName=Sazuke], Student [id=9, firstName=Haruno, lastName=Sakura]]
- Cek pada databases:
mysql> select * from classes;
+----+------------+------------+
| id | class_name | teacher_id |
+----+------------+------------+
| 1 | Kelas 10 | 5 |
+----+------------+------------+
1 row in set (0.00 sec)
mysql> select * from student;
+----+------------+-----------+----------+
| id | first_name | last_name | class_id |
+----+------------+-----------+----------+
| 1 | Uzumaki | Naruto | 1 |
| 2 | Uciha | Sazuke | 1 |
| 3 | Haruno | Sakura | 1 |
+----+------------+-----------+----------+
3 rows in set (0.01 sec)