Hi,
I have a resource (an Experiment, for instance), that requires an
exact number of Players to play, 5 say. The idea is that the
Experiment resource sits there accepting requests from Players to play
until it has the correct number of Players - no more and no less.
I've implemented this as follows:
a Player requests to play by visiting: experiment/{experiment_name}/
start
the associated view calls an add_player(p) method on the named
Experiment object
class Experiment:
players = models.ManyToManyField(Player...)
required_players = models.PositiveIntegerField()
...
def add_player(self,p):
if |self.players| < self.required_players then
self.players.add(p)
if |self.players| == required_players:
# ....
self.save()
My problem is: is there any way to make this function atomic? i.e.
consider the case where the Experiment only requires one more Player,
and two Players make requests at the same time, then provided the
second passes the |Players| < 5 test before the first writes, then
they'll both be added, violating my Model.
>From what I understand of django.db.transaction, this wouldn't protect
me from the above situation, since it only protects commits to the
database. Is that correct?
Thanks for your time,
Ian Murray.
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