ok, so it appears the best way is to query the key only. I have set
it up to do that, except now I'm having an issue where the parent
object is not storing the child's key.
Below is to show how I set up my classes to save a reference to the
child classes
@PersistenceCapable
class parent {
@PrimaryKey
@Persistent
Key key;
//other private variables
@Persistent
Key childKey;
}
The issue is that when I make the parent class persistent, for some
reason the child key becomes null. It is set in the constructor as
the value of the child's key (I call a static method to create the
child object then return the key). I know the key returned is not
null through some debugging.
Why would a persistent Key stay transient? The docs say that Keys are
persistent capable
On Dec 21, 4:32 pm, Mike <[email protected]> wrote:
> You can query the key only, hope this helps.
>
> http://code.google.com/appengine/docs/python/datastore/queriesandinde...
>
> On Dec 21, 8:51 pm, Jess Evans <[email protected]> wrote:
>
>
>
> > Be wary of a try/get/catch/persist combo. I was doing this initially, but
> > found it triggered a memory leak. I resorted to a query by business key. I
> > can't confirm whats most efficient. It's certainly not in terms of index
> > storage overhead. I just wanted to throw out the warning.
>
> > On Dec 21, 2009 12:08 PM, "t3jem" <[email protected]> wrote:
>
> > Ok,
>
> > So I'm writing my first game using the Google App Engine and have been
> > finding that using RPC and the datastore is much different than I'm
> > use to. I've managed to get along, but I'm pretty stuck on this one,
> > I can't find it anywhere.
>
> > My problem is, I need to be able to create a new object with a unique
> > ID when a new user logs into the game. I was doing this by randomly
> > generating a key and then using a query to the datastore to retrieve
> > an object by that ID. If nothing turns up then I persist the new
> > object with that ID. I understand that with an exceedingly great
> > amount of users this method could become a bit slow, but I don't
> > intend to have more than 1000 objects of this type in the datastore so
> > I don't foresee any problems with this method (please tell me if I'm
> > terribly mistaken).
>
> > I get my error when I go to attempt a retrieval of the missing object
> > from the datastore. I use PersistenceManager.getObjectById(foo.class,
> > Key)
>
> > when my program reaches the call it throws a
> > NucleusObjectNotFoundException. I understand this is probably normal
> > behavior, the problem is, I can't seem to find a way to check if the
> > key already exists in the datastore or not.
>
> > Is there a cheap way to check for a key? the only other method I can
> > think of is to get a collection of all the objects of that class and
> > check the created key against all existing ones, but that seems much
> > to expensive.
>
> > Thank you for your time
>
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