Hi,
entity group is not useful at rollback but rather limits you to which
updates you can do: all the entities you touch in a single transaction
must be in the same entity group.
So, designing your groups properly is a key design issue in GAE to
avoid unnecessary complexity when you later need to update at once
entities that you created before in various groups.
regards
didier
On May 30, 7:57 am, Jacob <jacob.rho...@gmail.com> wrote:
> I am writing some code that needs to do a rollback on a secondary
> object/table should the transaction fail, I believe this can be done
> via entity groups, however I am not sure if this is how it would be
> implemented. I have written some sample code to check if what I would
> be doing is correct?
>
> Would the following code ensure the "Account" object is never updated
> if the insert of the "TransactionRecord" object fails.
>
> public void addTransaction(String account, Double value, String
> description, Date date) throws EntityNotFoundException {
> DatastoreService datastore =
> DatastoreServiceFactory.getDatastoreService();
>
> int retries = 3;
> while (true) {
> Transaction txn = datastore.beginTransaction();
> try {
>
> // Update the bank balance
> Key key = KeyFactory.createKey("Account",
> account);
> Entity e = datastore.get(key);
> Double balance = (Double)
> e.getProperty("balance");
> balance += value;
> e.setProperty("balance", value);
> datastore.put(e);
>
> // Record transaction details
> Entity d = new Entity("TransactionRecord",
> key);
> d.setProperty("account_key", key);
> d.setProperty("date", date);
> d.setProperty("value", value);
> d.setProperty("description", description);
>
> txn.commit();
> break;
> } catch (ConcurrentModificationException e) {
> if (retries == 0)
> throw e;
> --retries;
> } finally {
> if (txn.isActive())
> txn.rollback();
> }
> }
>
> }
>
> Thanks for any feedback!
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