Stored data in GAE - Entity cannot have a long primary key and be a child

Question

We have difficulty saving data in our Google App Engine project, we have the classes "Client", "Booking" and "Room".

Our goal is to correlate the relationship between them, with a one-to-many relationship from customer to reservation and a one-to-many relationship from room to same reservation.

The exception is:

Error in metadata for no.hib.mod250.asm2.model.Reservation.id: cannot have the primary key java.lang.Long and be a child (the owner 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 shows, you cannot use a long primary key if your object is a child of the object, which in this case is true. Instead, use a key or an encoded string as the primary key. See here for more details.

You should probably also read child objects and relationships .