user424174 user424174 - 2 months ago 17
Java Question

Query Google App Engine Datastore with Key.Id

I'm deploying a simple Java app to Google App Engine.

I have a simple JPA Entity containing a Key as my generated ID.

import javax.persistence.*;

@Entity
public class MyEntity
{
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private com.google.appengine.api.datastore.Key key;
...


Once I persisted this object. I can view the key's ID like so...

long id = entity.getKey().getId();


Do you know how I can I use the same Id to get my entity back? Something like this...

Query query = em.createQuery("SELECT e FROM MyEntity e WHERE e.key.id = :myId");
query.setParameter("myId", id);


The above doesn't work. I know I can get it back by passing in the Key as the parameter, but I'd like to know if I could use the long id instead.

Answer

Found the solution, create a Key using the KeyFactory and pass in the ID. Then Query on Key.

Key key = KeyFactory.createKey(MyEntity.class.getSimpleName(), id);