Object isnt saved for Unowned Many to Many relation

Question

I have an unowned Many to Many relationship setup in JDO by adding the List in both the Persistence Capable objects. For the sake of explaining my problem lets call these two entities with .

EntityA and EntityB

Now, when i have a new Object of EntityB to be attached to the Object of EntityA, i append that Key to the EntityA object and call makePersistent on it, which saves the object. I verified that by printing it on the console.

Since, this is a Many to Many relation, i have to do the same on the other end of the relation as well. So, i fetch all the objects of EntityB which are referred by EntityA using select from " + clazz.getName()+ " where :keys.contains(key) and passing it the List of Keys which are present in Object of EntityA.

The problem that i encounter is, the objects returned back are Hollow, and hence they dont get saved into the datastore even if i append the EntityA keys to the fetched objects.

I am a newbie in JDO and GAE, and have been facing this problem since yesterday. Can someone please shed some light on this? I can provide sample code if needed too.

Answer 1

Here is the code

@PersistenceCapable
public class Objective {
@PrimaryKey
@Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY)
private Key key;
@Persistent
private boolean active;
@Persistent
private int corporate;
@Persistent
private String nameOfObjective;
@Persistent
private String shortDescription;
@Persistent
private int status;

@Persistent
private List<Key> scoreCardKeys; //List of Keys of Scorecards.


@PersistenceCapable
public class Scorecard {

@PrimaryKey
@Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY)
private Key key;

@Persistent
private boolean active;
@Persistent
private int corporate; // synonymous to being public 
@Persistent
private Date creationDate;
@Persistent
private String nameOfScorecard;
@Persistent
private String shortDescription;

@Persistent
private Key createdUserKey;

@Persistent
private List<Key> objectiveKeys; // List of Keys of Objectives

Objective and Scorecard entities are in an unowned Many to Many relation

Here is the processor method which will update a Scorecard.

public ScoreCardRepresentation updateScoreCard(ScoreCardRepresentation scoreCardRepresentation) {
    Scorecard scoreCard = scoreCardTransformer
            .transformRtoEForSave(scoreCardRepresentation);

    scoreCard.setCreationDate(new Date());

    Scorecard updatedScoreCard = scoreCardDAO.saveScoreCard(scoreCard); /*     Update the scorecard, this already has the list of Key of Objectives in it, Hence blindly save it. */

/* Update the Key of the scorecard in the Objectives too */       
updateRelatedObjectivesToScoreCard(scoreCardRepresentation,updatedScoreCard);




private void updateRelatedObjectivesToScoreCard(
        ScoreCardRepresentation scoreCardRepresentation,
        Scorecard updatedScoreCard) {
List<String> addedObjectivesIds =  scoreCardRepresentation.getAddedObjectiveKeys();
List<String> deletedObjectivesIds =  scoreCardRepresentation.getRemovedObjectiveKeys();

    // Add ScoreCard to the newly added Objectives
    if(addedObjectivesIds != null && addedObjectivesIds.size()>0){

Scorecard sc = scoreCardDAO.findScoreCardById(Scorecard.class, updatedScoreCard.getKey());
        List<Key> objKeys = sc.getObjectiveKeys();

        List<Objective> objectives = objectiveDAO.findObjectivesByKeys(Objective.class,objKeys);

// This uses the query select from " + clazz.getName()+ " where :keys.contains(key)

        for(Objective obj : objectives){
            List<Key> scoreCardKeys = obj.getScoreCardKeys();
            if(scoreCardKeys != null){
                scoreCardKeys.add(sc.getKey());
            } else { 
                scoreCardKeys = new ArrayList<Key>();
                scoreCardKeys.add(sc.getKey());
            }
            obj.setScoreCardKeys(scoreCardKeys);
            Objective updatedObjective = objectiveDAO.saveObjective(obj);
            System.out.println(new ObjectiveProcessor().viewObjective(KeyFactory.keyToString(obj.getKey())));
        }
    }

    //Remove Scorecard entries from Objective. 
    if(deletedObjectivesIds != null && deletedObjectivesIds.size()>0){
        List<Objective> objectives = objectiveDAO.findObjectivesByIds(Objective.class,deletedObjectivesIds);
        for(Objective obj : objectives){
            List<Key> scoreCardKeys = obj.getScoreCardKeys();
            if(scoreCardKeys != null){
                scoreCardKeys.remove(updatedScoreCard.getKey());
            } 
            obj.setScoreCardKeys(scoreCardKeys);
        }
    }
}

All i have been able to realise is that when i get back the Objectives using **findObjectivesByKeys** i am getting back hollow objects, so i have to call makeTransient on them to enable them for persistence, else they just ignore the makePersistent method call.