Hi all,
As the following document(54p) says,
journal and last committed timestamp are co-located with a root entity
of an entity group.
http://snarfed.org/space/datastore_talk.html
But, an entity group that does not have a root entity seem to support
transaction.
How does it work?
I tried the following code on production server:
DatastoreService ds = DatastoreServiceFactory.getDatastoreService();
Key parentKey = KeyFactory.createKey("Parent", 1);
Key child1Key = KeyFactory.createKey(parentKey, "Child", 1);
Key child2Key = KeyFactory.createKey(parentKey, "Child", 2);
Transaction tx1 = ds.beginTransaction();
ds.put(tx1, new Entity(child1Key));
Transaction tx2 = ds.beginTransaction();
ds.put(tx2, new Entity(child2Key));
tx1.commit();
try {
tx2.commit();
} catch (ConcurrentModificationException e) {
System.out.println(
"An entity group that does not have a root entity supports
transaction.");
}
try {
ds.get(parentKey);
} catch (EntityNotFoundException e) {
System.out.println("There is no root entity.");
}
ds.delete(child1Key);
App Engine SDK version:1.2.8
Thanks,
Yasuo Higa
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