Table per concrete class inheritance strategy

Remarks#

Vehicle, TransportationVehicle and PassengerVehicle are abstract classes and they will not have separate table in database.
Truck, Car and Bike are concrete classes so they will be mapped to corresponding tables. These tables should include all the fields for classes annotated with @MappedSuperClass because they don’t have corresponding tables in database.
So, Truck table will have columns to store fields inherited from TransportationVehicle and Vehicle.
Similarly, Car and Bike will have columns to store fields inherited from PassengerVehicle and Vehicle.

Full example can be found here

Table per concrete class inheritance strategy

We will take vehicle hierarchy example as depicted below.

Vehicle.java

package com.thejavageek.jpa.entities;

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

@Entity
@Inheritance(strategy = InheritanceType.TABLE_PER_CLASS)
public abstract class Vehicle {

    @TableGenerator(name = "VEHICLE_GEN", table = "ID_GEN", pkColumnName = "GEN_NAME", valueColumnName = "GEN_VAL", allocationSize = 1)
    @Id
    @GeneratedValue(strategy = GenerationType.TABLE, generator = "VEHICLE_GEN")
    private int idVehicle;
    private String manufacturer;

    public int getIdVehicle() {
        return idVehicle;
    }

    public void setIdVehicle(int idVehicle) {
        this.idVehicle = idVehicle;
    }

    public String getManufacturer() {
        return manufacturer;
    }

    public void setManufacturer(String manufacturer) {
        this.manufacturer = manufacturer;
    }

}

TransportationVehilcle.java

package com.thejavageek.jpa.entities;

import javax.persistence.MappedSuperclass;

@MappedSuperclass
public abstract class TransportationVehicle extends Vehicle {

    private int loadCapacity;

    public int getLoadCapacity() {
        return loadCapacity;
    }

    public void setLoadCapacity(int loadCapacity) {
        this.loadCapacity = loadCapacity;
    }

}

Truck.java

package com.thejavageek.jpa.entities;

import javax.persistence.Entity;

@Entity
public class Truck extends TransportationVehicle {

    private int noOfContainers;

    public int getNoOfContainers() {
        return noOfContainers;
    }

    public void setNoOfContainers(int noOfContainers) {
        this.noOfContainers = noOfContainers;
    }

}

PassengerVehicle.java

package com.thejavageek.jpa.entities;

import javax.persistence.MappedSuperclass;

@MappedSuperclass
public abstract class PassengerVehicle extends Vehicle {

    private int noOfpassengers;

    public int getNoOfpassengers() {
        return noOfpassengers;
    }

    public void setNoOfpassengers(int noOfpassengers) {
        this.noOfpassengers = noOfpassengers;
    }

}

Car.java

package com.thejavageek.jpa.entities;

import javax.persistence.Entity;

@Entity
public class Car extends PassengerVehicle {

    private int noOfDoors;

    public int getNoOfDoors() {
        return noOfDoors;
    }

    public void setNoOfDoors(int noOfDoors) {
        this.noOfDoors = noOfDoors;
    }

}

Bike.java

package com.thejavageek.jpa.entities;

import javax.persistence.Entity;

@Entity
public class Bike extends PassengerVehicle {

    private int saddleHeight;

    public int getSaddleHeight() {
        return saddleHeight;
    }

    public void setSaddleHeight(int saddleHeight) {
        this.saddleHeight = saddleHeight;
    }

}

Database representation will be as below