Hibernate - One to One using Annotations

One to One mapping can also be achieved in Hibernate and it is a bit easier than the XML mapping.

As stated for XML mapping, say an 'Employee' has only one 'Address' and both 'Employee' and 'Address' are Entities.

In that case we will be going for a 'one to one' mapping.

Let us see the 'Employee' class:

class Employee {

String id;
String name;

@OneToOne(Cascade=CascadeType.ALL)
Address address;

---Getters & Setters---
}

An 'Employee' can have only one 'Address'. So, in the 'Employee' class we have put:

Address address;

Just above the 'Address address' we have put '@OneToOne' annotation and we do not need to specify anything in the mapping file.

The 'Address' class is defined below.

class Address{
@Id
@Column(name="ADDRESS_ID")
int addressId;

@Column(name="STREET_NAME")
String streetName;

@Column(name="CITY")
String city;

@Column(name="PIN_CODE")
String pinCode;

@OneToOne
Employee employee;

---Getters & Setters---
}

Same logic applies for 'Address' class as well. i.e. There is an One to One mapping and we have put '@OneToOne' just above the Employee reference.

Employee employee;

And our mapping is done.

Now, we will be writing the main class where we will be saving the 'Employee' data and its corresponding 'Address' data to the database using Hibernate.

import org.hibernate.Session;
import org.hibernate.Transaction;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;

public class HibernateSave {
public static void main(String[] args) {

static SessionFactory sessionFactory = new Configuration().configure().buildSessionFactory();
Session session = sessionFactory.openSession();
session.beginTransaction();

Address address = new Address();

Address address = new Address();
address.setStreetName("Walls Street");
address.setCity("Delhi");
address.setPinCode("110012");

Employee employee = new Employee();
employee.setId(1);
employee.setName("Joe");
employee.setAddress(address);
session.save(employee);

//session.save(localAddress);
//Don't have to write the above statement as cascade="all" is set in the mapping file.

session.getTransaction().commit();

session.close();
sessionFactory.close();
}
}

EMPLOYEE

ID	NAME
1	Joe

ADDRESS

ID	STREET_NAME	CITY	PIN_CODE
1	Walls street	Delhi	110012

So, 'ID' column in the 'EMPLOYEE' table is the foreign key 'ID' in 'ADDRESS' table.

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