Question

I’m trying to model my Java app engine objects through list properties for fast efficient querying. Can I improve this code at all?

I don’t really want to migrate over to Objectify.

Here’s the code to retrieve it:

query = persistenceManager.newQuery(HuddleCreatorIndex.class, ":p.contains(creator)");
List<HuddleCreatorIndex> myCreatorIndexList = (List<HuddleCreatorIndex>) query.execute(KeyFactory.createKey(Contact.class.getSimpleName(), fbUserId));
if (myCreatorIndexList.size() > 0) {
    Set<Long> huddles = myCreatorIndexList.get(0).getHuddles();
    //THIS FOR LOOP DID THE TRICK, why is this necessary?  Never saw it in any examples
    for (Long huddleKey : huddles)
        alist.add(persistenceManager.newObjectIdInstance(Huddle.class, huddleKey));
    Collection<Huddle> huddlesICreated = persistenceManager.getObjectsById(huddles);
    allMyHuddles.addAll(huddlesICreated);
}

Here’s the rest of the supporting code showing how the objects are originally stored, and also the relevant model classes.

This code called to on creation of a Huddle (and this correctly sets up all the objects in the datastore)

txn.begin();
//First, create the Huddle, this main model class
newHuddle.setInvitees(inviteeList);
newHuddle = pm.makePersistent(newHuddle);
huddleId = newHuddle.getId();

//Now create the first index
HuddleIndex newIndex = new HuddleIndex();               
newIndex.setParent(KeyFactory.createKey(Huddle.class.getSimpleName(), newHuddle.getId()));
newIndex.setInvitees(inviteeList);
pm.makePersistent(newIndex);

//And finally, create the other index
Query query = pm.newQuery(HuddleCreatorIndex.class);
query.setFilter(":p.contains(creator)");
List<HuddleCreatorIndex> list = (List<HuddleCreatorIndex>) query.execute(creator.getId());
if (list != null && list.size() > 0) {
    HuddleCreatorIndex thisIndex = list.get(0);
    Set<Key> huddles = thisIndex.getHuddles();
    huddles.add(KeyFactory.createKey(Huddle.class.getSimpleName(), newHuddle.getId()));
    thisIndex.setHuddles(huddles);
} else {
    HuddleCreatorIndex newCreatorIndex = new HuddleCreatorIndex();
    newCreatorIndex.setCreator(creator.getId());
    Set<Long> huddleSet = new HashSet<Long>(1);                   
    huddleSet.add(newHuddle.getId());
    newCreatorIndex.setHuddles(huddleSet);
    pm.makePersistent(newCreatorIndex);
}
txn.commit();

Here’s my actual model object with the real data

@PersistenceCapable(identityType = IdentityType.APPLICATION, detachable="true")
public class Huddle {

    @PrimaryKey
    @Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY)
    private Long id; 

    private Key creator;
    private String name;
    private Date whenTimeStamp;
    private Date creationTimeStamp;
    private String userIdType;
    private Set<Key> invitees;
    private String status;
    private Set<Key> choices;
    private List<Vote> votes;

    //setters, getters, and constructor omitted
}

My index object to make the list property magic happen

@PersistenceCapable(identityType = IdentityType.APPLICATION, detachable="true")
public class HuddleCreatorIndex {

    @PrimaryKey
    @Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY)
    private Key id; 
    private Key creator;
    private Set<Long> huddles;
    //setters, getters, and constructor omitted
}

Answer 1

Whats wrong with the code ?

You have @Persistent plastered all over the place (implied by Googles docs admittedly, but then best not to believe them), you don’t need that … all standard types are by default persistent (as per the JDO spec, and indeed extended by Google’s own code to make their Key class etc as persistent by default). Makes the class look much more normal.

You’re calling makePersistent, yet the object being persisted is in what “state” ? JDOHelper.getObjectState(obj) tells you. If it is already managed then there is no need to do that … the whole point of that bytecode enhancement process, to detect changes. Obviously a nontransactional update will not happen immediately. You don’t say if using a transaction around that.

Look in the Log for the retrieve, tells you way more than anyone here can.

Not using v2.0 of the GAE JDO plugin probably too; anything earlier than that is very old and not maintained.