Implicit transactions are a separate issue (and a terrible idea).
When the low-level api starts a transaction, it stores this txn as a thread
local. The get()/put()/etc methods that don't have a transaction are
effectively this logic:
Entity get(Key key) {
if (there is a thread local txn)
return this.get(theThreadLocalTxn, key);
else
return this.get(null, key);
}
Passing in null is the only way to guarantee that you're making a call
without a transaction.
This thread-local transaction stuff helps support the JDO/JPA plugin but
it's a bit of a mess if you use the low-level API. My advice is not to use
it at all - avoid the methods that don't have a txn parameter and pass null
in when you don't have/want a transaction. Hide this behind a facade.
Jeff
On Fri, Oct 21, 2011 at 5:23 AM, Mos <[email protected]> wrote:
> I'm a bit confused:
> Following some examples and looking at the API of the DatastoreService
> it seems to be required to use the overloaded methods whenever
> transactional behavior is required.
> In other words: The current transaction needs to be specified on put() und
> get() methods like this:
>
> Transaction txn = datastore.beginTransaction();
> // ....
> Entity employee = datastore.get(txn, employeeKey);
> employee.setProperty("vacationDays", 10);
> datastore.put(txn, employee);
> txn.commit();
>
> But when looking at the official Google docs, there seems to be no need for
> specifying the
> transaction explicitly:
>
> http://code.google.com/intl/de-DE/appengine/docs/java/datastore/transactions.html
> ?
>
> Can someone explain this? Is this an issue with "implicit transaction"
> behavior? How does it work?
>
> Thanks a lot
> Mos
>
>
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