Java EE - [class ] 作为关系属性中的目标实体

Question

我正在开发一个具有持久性的 Java EE 应用程序。

我的Car类有一些Reservation，并且Reservation类扩展了Quote类。

出于某种原因，Reservation 不是实体类。我的猜测是继承有问题，但我似乎无法弄清楚。

汽车看起来像这样:

@Entity
public class Car {

    @Id
    private int id;

    @OneToOne(cascade=PERSIST, mappedBy="CarType")
    private CarType type;

    @OneToMany(cascade=REMOVE, mappedBy="Quote")
    private Set<Reservation> reservations;

    public Car() {}

    . 
    .
    .

    public boolean equals(Object otherObject) {
        ...
    }

    public int hashCode() {
        ...
}

预订看起来像这样

@Entity
@Table(name = "Reservation")
public class Reservation extends Quote {

    @Id
    @GeneratedValue(strategy=AUTO)
    @Column(name="reservationId")
    private int reservationId;

    private int carId;

    public Reservation() {}

    public Reservation(Quote quote, int carId) {
        super(quote.getCarRenter(), quote.getStartDate(), quote.getEndDate(), 
            quote.getRentalCompany(), quote.getCarType(), quote.getRentalPrice());
        this.carId = carId;
    }

    .
    .
    .

    public boolean equals(Object otherObject) {
        ...

    }

    public int hashCode() {
        ...
    }
}

引用看起来像这样:

@MappedSuperclass
public class Quote implements Serializable {

    @Id
    @GeneratedValue(strategy=AUTO)
    @Column(name="quoteId")
    private int quoteId;

    @Temporal(DATE)
    private Date startDate;
    @Temporal(DATE)
    private Date endDate;
    private String carRenter;
    private String rentalCompany;
    private String carType;
    private double rentalPrice;

    public Quote() {}

    public Quote(String carRenter, Date start, Date end, String rentalCompany, String carType, double rentalPrice) {
        ...
    }

    .
    .
    .

    @Override
    public int hashCode() {
        ...
    }

    @Override
    public boolean equals(Object obj) {
        ...    
    }
}

为什么 Reservation 不是正确的实体类？

Answer 1

实体 Reservation 必须删除 @id，因为女儿从父类(super class)继承它

指定一个类，其映射信息应用于从它继承的实体。映射的父类(super class)没有为其定义单独的表。