On Mar 15, 9:28 am, Iap <[email protected]> wrote:
>
> The other suggestion is the "transaction". I encountered many exceptions
> while putting the step 3.2, 3.3 to a transaction.
> Such as "nested transaction is not allowed","Cannot operate on different
> entity groups","must be an ancestor...".
> Because the transaction has so much limitation, it seems not realistic to
> use transaction.
Something like this?
class Queued(db.Model):
done = db.BooleanProprty(required=True, default=False)
order = db.DateTimeProperty(required=True, auto_now_add=True)
work = db.TextProperty() # whatever...
@classmethod
def get_next(cls):
next = None
while next is None:
next = cls.all().filter('done =', False) \
.order('order').fetch(1)
if next is None:
return None
next = cls._mark_done_transactionally(next)
return next
@classmethod
def _mark_done_transactionally(cls, queued):
def txn(queued):
queued = db.Get(queued.key())
if queued.done:
return None
queued.done = True
queued.put()
return queued
return db.run_in_transaction(txn, queued)
some_work_to_do = Queued.get_next()
if some_work_to_do:
print 'Do once: %s' % some_work_to_do.work
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