表每具体类继承策略

我们将采用车辆层次结构示例，如下所示。

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;
    }

}

数据库表示如下