[GAE - Objectify]: LinkedHashMap doesn't respect key's order - google-app-engine

Question

I'm working with Objectify to access DataStore in a Google App Engine application.
I have 2 Entities:
#Entity
public class Client {
#Id String id;
}
#Entity
public class Queue {
#Index #Id String name;
#Load LinkedHashMap<String,Ref<Client>> clientsInQueue;
}
In a transaction, i do something like this:
Client newClient = new Client(...);
ofy().save().entity(newClient);
Queue selectedQueue = ofy().load().type(Queue.class).id(queueName).now();
selectedQueue.getClientsInQueue().put(newClient.getId(), Ref.create(newClient));
But when i try to print all the elements in the LinkedHashMap, i noticed the elements is in the exactly reverse order.
For example if i add 2 Clients in the LinkedHashMap and save it, like this:
Queue selectedQueue = new LinkedHashMap<String,Ref<Client>>();
String id1 = "id1";
Client c1 = new Client(id1);
ofy().save().entity(c1);
String id2 = "id2"
Client c2 = new Client(id2);
ofy().save().entity(c2);
selectedQueue.getClientsInQueue().put(c1.getId(), Ref.create(c1));
selectedQueue.getClientsInQueue().put(c2.getId(), Ref.create(c2));
ofy().save().entity(selectedQueue);
Set<String> keys = selectedQueue.getClientsInQueue().keySet();
for(String key : keys){
Client c= selectedQueue.getClientsInQueue().get(key).get();
log.info("id: "+c.getId());
}
The result is:
id: id2
id: id1
Why i obtain this behavior ? I know that LinkedHashMap has to maintain the order of the keys! Is there any problem to use LinkedHashMap with GAE DataStore?
Thanks in advance.
Cheers,
Alessandro.

Answer 1

Fields of type Map<String, ?> are stored in the low level api as type EmbeddedEntity, the only map-like structure available as a property. This EmbeddedEntity is implemented as a non-linked HashMap. Consequently, there is no way for Objectify to preserve order.
I'll make a note of this in Objectify's documentation. If you would like this behavior to change, open up an issue in GAE's issue tracker requesting "Entity and EmbeddedEntity should use a LinkedHashMap to preserve order".