Problem with persisting data in Google Application Engine

Question

Hi, we are having a hard time persisting data in our google app project, we have the classes "Customer" "Reservation" and "Room".

Our goal is to map a relation between these, with a one-to-many relation from Customer to Reservation and a one-to-many relation from Room to the same Reservation.

The exception we get is: Error in meta-data for no.hib.mod250.asm2.model.Reservation.id: Cannot have a java.lang.Long primary key and be a child object (owning field is no.hib.mod250.asm2.model.Customer.res).

Our code is as follows:

Customer.java
@PersistenceCapable(identityType=IdentityType.APPLICATION)  
public class Customer implements Serializable {  
    @PrimaryKey  
    @Persistent(valueStrategy=IdGeneratorStrategy.IDENTITY)  
    private Long id;  
    (...) 
    //an customer has one or more reservations.  
    @Persistent(mappedBy="customer")  
    private List <Reservation> res;  
    (...)  
}  

Room.java  
@PersistenceCapable(identityType=IdentityType.APPLICATION)  
public class Room implements Serializable {  
    @PrimaryKey  
    @Persistent(valueStrategy=IdGeneratorStrategy.IDENTITY)  
    private Long id;  
    (...)  
    //a room has one or more reservations  
    @Persistent(mappedBy="room")  
    private List<Reservation> res;  
    @Persistent  
    private Hotel hotel;  
    (...)  
}   

Reservation.java  
@PersistenceCapable(identityType=IdentityType.APPLICATION)  
public class Reservation implements Serializable {  
    @PrimaryKey  
    @Persistent(valueStrategy=IdGeneratorStrategy.IDENTITY)  
    private Long id;  
    (...)  
    @Persistent  
    private Room room;  
    @Persistent  
    private Customer customer;  
    (...)  
}

Answer 1

As the message suggests, you can't use a long as your primary key if your entity is a child entity, which is true in this case. Instead, use a key or encoded string as your primary key - see here for details.

You should probably also read up on child objects and relationships.