GAE datastore array initialization throw: FK Arrays not supported

Question

I’m trying to save an array object in an entity class, which I would like to store in the GAE datastore. Sadly I get a exception, while I’m trying to initialize the array.

I get this error:

java.lang.UnsupportedOperationException: FK Arrays not supported.

My class looks like this:

@Entity
public class Game {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Key key;
    ...
    @Persistent
    private Profile[] players = new Profile[4];
    ...
    public void setPlayers(Profile player) {
        if (pcount.intValue() < 4) {
            this.players[pcount] = player; //Here I get the exception
            pcount = Integer.valueOf(pcount.intValue() + 1);
        }
    }
}

Profile is also a entity class.

What went wrong? How could i fix this. It would be greate if someone could explain it to me!

Answer 1

You need to annotate your Profile entity as @Embeddable and in your Game entity to annotate the players field as @Embedded. For detailed info on JPA annotations take a look at JPA 2 Annotations. In this way, all the Profile fileds will be shown as inline fields of your Game entity. If you just want to keep a reference from your Game entity to your Profile entities, you can use an array of Key and not Profile. For example,

private Key[] players = new Key[4];

Hope this helps.