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Component - Set Mapping using Annotations

If we use annotations, we do not have to write the extra mapping files for 'Employee' and 'Address'. We can configure the mapping in the Class itself.

Note : While dealing with components we have put the 'Employee' record and its corresponding 'Address' record in the same table i.e. EMPLOYEE table. But in this case we can have multiple 'Address' for a single 'Employee'. Although, 'Address' is a Component still we need to have two different tables i.e 'EMPLOYEE' AND 'ADDRESS' to avoid data duplication.

Let us see the example below:

So, an 'Employee' can have multiple 'Address'.

class Employee{
int id;
String name;

@ElementCollection
@JoinTable(name="ADDRESS",JoinColumns=@JoinColumn(name="ID"))
Set <Address> addressSet = new HashSet <Address> ();
---Getters & Setters---
}

We have used 'Set' to hold multiple 'Address'.

Set <Address> addressSet = new HashSet <Address> ();

@ElementCollection above the 'Set' tells Hibernate that a separate 'ADDRESS' table should be created.
And the

@JoinTable(name="ADDRESS", JoinColumns=@JoinColumn(name="ID"))

tells Hibernate that the name of the table should be 'ADDRESS' and the foreign key should be named as 'ID'.

Similarly, the 'Address' class looks like :

class Address{
String streetName;
String city;
String pinCode;
---Getters & Setters---
}

Next, let us write 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();

Set<Address> addressSet = new HashSet<Address> ();

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

addressSet.add(localAddress);

Address permanentAddress = new Address();
permanentAddress.setStreetName("Murugeshpalya");
permanentAddress.setCity("Bangalore");
permanentAddress.setPinCode("560019");

addressSet.add(permanentAddress);

Employee employee = new Employee();
employee.setId(1);
employee.setName("Joe");
employee.setAddressSet(addressSet);
session.save(employee);

session.getTransaction().commit();

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

Below is the output:

EMPLOYEE

ID	NAME
1	Joe

ADDRESS

ID	STREET_NAME	CITY	PIN_CODE
1	Walls street	Delhi	110012
1	Murugeshpalya	Bangalore	560019

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