17 - Implementing Inheritance

We'll understand how to configure entity classes that have an inheritance hierarchy.

HibernateTest.java

package org.yash.hibernate;

import org.hibernate.Session;

import org.hibernate.SessionFactory;

import org.hibernate.cfg.Configuration;

import org.yash.dto.FourWheeler;

import org.yash.dto.TwoWheeler;

import org.yash.dto.Vehicle;

public class HibernateTest {

      public static void main(String args[]) {

            Vehicle vehicle = new Vehicle();

            vehicle.setVehicleName("Car");

            TwoWheeler bike = new TwoWheeler();

            bike.setVehicleName("Bike");

            bike.setSteeringHandle("Bike Steering Handle");

            FourWheeler car = new FourWheeler();

            car.setVehicleName("Porsche");

            car.setSteeringWheel("Porsche Steering Wheel");

            SessionFactory sessionFactory = new Configuration().configure()

                        .buildSessionFactory();

            Session session = sessionFactory.openSession();

            /* It is used to save all the objects and to define single unit of work */

            session.beginTransaction();

            session.save(vehicle);

            session.save(bike);

            session.save(car);

            session.getTransaction().commit();

            session.close();

      }

}

Vehicle.java

package org.yash.dto;

import javax.persistence.Entity;

import javax.persistence.GeneratedValue;

import javax.persistence.Id;

import javax.persistence.ManyToOne;

import org.hibernate.annotations.NotFound;

import org.hibernate.annotations.NotFoundAction;

@Entity

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;

                }

}

TwoWheeler.java

package org.yash.dto;

import javax.persistence.Entity;

@Entity

public class TwoWheeler extends Vehicle {

      private String SteeringHandle;

      public void setSteeringHandle(String steeringHandle) {

            SteeringHandle = steeringHandle;

      }

      public String getSteeringHandle() {

            return SteeringHandle;

      }    

     

}

FourWheeler.java

package org.yash.dto;

import javax.persistence.Entity;

@Entity

public class FourWheeler extends Vehicle {

            private String steeringWheel;

            public void setSteeringWheel(String steeringWheel) {

                  this.steeringWheel = steeringWheel;

            }

            public String getSteeringWheel() {

                  return steeringWheel;

            }

     

}

hibernate.cfg.xml

<?xml version='1.0' encoding='utf-8'?>

<!DOCTYPE hibernate-configuration PUBLIC

        "-//Hibernate/Hibernate Configuration DTD 3.0//EN"

        "http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">

<hibernate-configuration>

    <session-factory>

        <property name="connection.driver_class">

            org.postgresql.Driver

        </property>

        <property name="connection.url">

            jdbc:postgresql://localhost:5433/hibernatedb

        </property>

        <property name="connection.username">postgres</property>

        <property name="connection.password">admin</property>

        <!-- JDBC connection pool (use the built-in) -->

        <property name="connection.pool_size">1</property>

        <!-- SQL dialect -->

        <property name="dialect">

            org.hibernate.dialect.PostgreSQLDialect

        </property>

        <!-- Enable Hibernate's automatic session context management -->

        <property name="current_session_context_class">thread</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> 

<!-- create / update -->

   

          <!-- Names the annotated entity class -->

            <mapping class="org.yash.dto.UserDetails"/>    

            <mapping class="org.yash.dto.Vehicle"/>  

            <mapping class="org.yash.dto.TwoWheeler"/>     

            <mapping class="org.yash.dto.FourWheeler"/>    

           

    </session-factory>

</hibernate-configuration>