Table Per Class Inheritance

In this post we will see the next strategy that hibernate uses while creating tables. In the strategy attribute of the @Inheritance annotation, if we use "TABLE_PER_CLASS", then hibernate creates a separate table for each entity. The below program explains how to achieve this.

<?xml version='1.0' encoding='utf-8'?>
<!DOCTYPE hibernate-configuration PUBLIC
        "-//Hibernate/Hibernate Configuration DTD 3.0//EN"
        "http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd">

<hibernate-configuration>

    <session-factory>

        <!-- Database connection settings -->
        <property name="connection.driver_class">oracle.jdbc.driver.OracleDriver</property>
        <property name="connection.url">jdbc:oracle:thin:@localhost:1521:xe</property>
        <property name="connection.username">hr</property>
        <property name="connection.password">hr</property>

        <!-- JDBC connection pool (use the built-in) -->
        <property name="connection.pool_size">1</property>

        <!-- SQL dialect -->
        <property name="dialect">org.hibernate.dialect.OracleDialect</property>

        <!-- Disable the second-level cache  -->
        <property name="cache.provider_class">org.hibernate.cache.NoCacheProvider</property>

        <!-- Echo all executed SQL to stdout -->
        <property name="show_sql">true</property>

        <!-- Drop and re-create the database schema on startup -->
        <property name="hbm2ddl.auto">create</property>

        <!-- Names the annotated entity class -->
        <mapping class="com.ram.dao.Vehicle"/>
        <mapping class="com.ram.dao.TwoWheeler"/>
        <mapping class="com.ram.dao.FourWheeler"/>

    </session-factory>

</hibernate-configuration>

File: com.ram.dao.Vehicle.java

package com.ram.dao;

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.Inheritance;
import javax.persistence.InheritanceType;

@Entity
@Inheritance(strategy=InheritanceType.TABLE_PER_CLASS)
public class Vehicle {
 @Id @GeneratedValue
 private int vehicleId;
 private String vehicleName;
 
 public int getVehicleId() {
  return vehicleId;
 }
 public void setVehicleId(int vehicleId) {
  this.vehicleId = vehicleId;
 }
 public String getVehicleName() {
  return vehicleName;
 }
 public void setVehicleName(String vehicleName) {
  this.vehicleName = vehicleName;
 }
}

File: com.ram.dao.TwoWheeler.java

package com.ram.dao;

import javax.persistence.Entity;

@Entity
public class TwoWheeler extends Vehicle {
 private String steeringHandle;

 public String getSteeringHandle() {
  return steeringHandle;
 }

 public void setSteeringHandle(String steeringHandle) {
  this.steeringHandle = steeringHandle;
 }
}

File: com.ram.dao.FourWheeler.java

package com.ram.dao;

import javax.persistence.Entity;

@Entity
public class FourWheeler extends Vehicle {
 private String steeringWheel;

 public String getSteeringWheel() {
  return steeringWheel;
 }

 public void setSteeringWheel(String steeringWheel) {
  this.steeringWheel = steeringWheel;
 }
}

File: com.ram.hibernate.TablePerClassExample.java

package com.ram.hibernate;

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

import com.ram.dao.FourWheeler;
import com.ram.dao.TwoWheeler;
import com.ram.dao.Vehicle;

public class TablePerClassExample {
 public static void main(String[] args) {
  Vehicle vehicle = new Vehicle();
  vehicle.setVehicleName("Car");
  
  TwoWheeler yamaha = new TwoWheeler();
  yamaha.setVehicleName("Yamaha");
  yamaha.setSteeringHandle("Yamaha steering handle");
  
  FourWheeler benz = new FourWheeler();
  benz.setVehicleName("Benz");
  benz.setSteeringWheel("Benz steering wheel");
  
  SessionFactory sessionFactory = new Configuration().configure().buildSessionFactory();
  Session session = sessionFactory.openSession();
  
  session.beginTransaction();
  session.save(vehicle);
  session.save(yamaha);
  session.save(benz);
  
  session.getTransaction().commit();
  session.close();
 }
}

Execute the TablePerClassExample.java and you get the below output.