Question

我有两个班，CarRentalCompany

@Entity
public class CarRentalCompany {

    private static Logger logger = Logger.getLogger(CarRentalCompany.class.getName());

    @Id
    private String name;

    @OneToMany(cascade = CascadeType.ALL)
    private List<Car> cars;

    @OneToMany(cascade = CascadeType.ALL, fetch = FetchType.EAGER)
    private List<CarType> carTypes = new ArrayList<>(); //TODO: kan betere datastructuur zijn

    /***************
     * CONSTRUCTOR *
     ***************/

    public CarRentalCompany()
    {
         // DEFAULT CONSTRUCTOR
    }

    public CarRentalCompany(String name, List<Car> cars) {
        logger.log(Level.INFO, "<{0}> Car Rental Company {0} starting up...", name);
        setName(name);
        this.cars = cars;
        for(Car car:cars) 
            carTypes.add(car.getType());
    }
    ...
}

和CarType

@Entity
public class CarType {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Key key;

    private String name;
    private int nbOfSeats;
    private boolean smokingAllowed;
    private double rentalPricePerDay;
    //trunk space in liters
    private float trunkSpace;

    /***************
     * CONSTRUCTOR *
     ***************/

    public CarType()
    {

    }

    public CarType(String name, int nbOfSeats, float trunkSpace, double rentalPricePerDay, boolean smokingAllowed) {
        this.name = name;
        this.nbOfSeats = nbOfSeats;
        this.trunkSpace = trunkSpace;
        this.rentalPricePerDay = rentalPricePerDay;
        this.smokingAllowed = smokingAllowed;
    }

运行该应用程序时，它将引发以下异常：

NucleusFatalUserException：尝试为孩子分配钥匙带有关键字的“ CarType（6614661952700416）”父级 “ CarRentalCompany（” Hertz“）”。父键是不可变的

我该怎么做才能正确获得CarType的密钥？

Answer 1

在添加CarType实体之前，您不是persisting您的CarRentalCompany实体。看到类似线程here。持久操作必须仅用于新实体。从未与数据库行关联的实体是新实体，这意味着数据库中没有与该实体匹配的表记录。

Google AppEngine密钥例外

1 个答案: