Advertisement
Google Ad Slot: content-top
Hibernate Many-to-One Mapping
A Many-to-One relationship means many child records are associated with one parent record.This is the inverse of @OneToMany.
For example:
- Many Employees belong to one Department.
- Many Orders belong to one Customer.
Create Read Update Delete (CRUD):
In this guide, we will implement CRUD (Create, Read, Update, Delete) operations for a Many-to-One Mapping using Hibernate.
Department and Employee class mentioned One-to-Many
HibernateUtil.java
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;
public class HibernateUtil {
private static final SessionFactory sessionFactory = buildSessionFactory();
private static SessionFactory buildSessionFactory() {
try {
return new Configuration()
.configure("hibernate.cfg.xml")
.addAnnotatedClass(Employee.class)
.addAnnotatedClass(Department.class)
.buildSessionFactory();
} catch (Throwable ex) {
System.err.println("SessionFactory creation failed: " + ex);
throw new ExceptionInInitializerError(ex);
}
}
public static SessionFactory getSessionFactory() {
return sessionFactory;
}
public static Session getSession() {
return sessionFactory.openSession(); // Opens a new session when needed
}
public static void shutdown() {
sessionFactory.close(); // Close SessionFactory when the application shuts down
}
}
Main.java
import org.hibernate.Session;
import org.hibernate.Transaction;
public class Main {
public static void main(String[] args) {
// Create
Session session = HibernateUtil.getSession();
Transaction transaction = session.beginTransaction();
// Create Department
Department department = new Department("IT");
// Create Employees
Employee emp1 = new Employee("Alice", department);
Employee emp2 = new Employee("Bob", department);
session.persist(department);
session.persist(emp1);
session.persist(emp2);
transaction.commit();
session.close();
// Read
Session session = HibernateUtil.getSession();
Employee employee = session.get(Employee.class, 1L);
System.out.println("Employee Name: " + employee.getName());
System.out.println("Department: " + employee.getDepartment().getName());
session.close();
// Update
Session session = HibernateUtil.getSession();
Transaction transaction = session.beginTransaction();
Employee employee = session.get(Employee.class, 1L);
if (employee != null) {
Department newDept = new Department("HR");
session.persist(newDept);
employee.setDepartment(newDept);
session.update(employee);
}
transaction.commit();
session.close();
// Delete
Session session = HibernateUtil.getSession();
Transaction transaction = session.beginTransaction();
Employee employee = session.get(Employee.class, 1L);
if (employee != null) {
session.delete(employee);
}
transaction.commit();
session.close();
HibernateUtil.shutdown(); // Close sessionFactory
}
}
Output
