Thanks!
Well, in JDO you can do:
Query q = pm.newQuery("select id from " + MyClass.class.getName());
I think __key__ can work too, but not sure.
On 4 July 2011 19:09, jMotta <jayrmo...@gmail.com> wrote:
> Thiago,
>
> Nowadays the amount of documentation and features of both interfaces are
> almost equals. Java has some characteristics that Python doesn't and
> vice-versa.
>
> But let's cope with your problem, the solution given by "objectuser" is
> valid and should work fine, the only problem is that you'll never be able to
> use transactions if the entities are not in the same entity group.
>
> A middle term between querying the real entity and just refering the id of
> it is to query and persist just the Key through:
>
> Query q = new Query("User").setKeysOnly();
>
>
> Combined with the filter that you may want and after that asking the
> datastore service (because I haven't found any hook in the JDO API to ask
> for the keys) for the keys and using it as the argument to your new
> LoginHistory entity.
>
> And your english is not bad. Bwt, I'm brazilian too! :)
>
> *Jayr Motta*
> Software Developer
> *
> *
> I'm on
> BlackBeltFactory.com<http://www.blackbeltfactory.com/ui#!User/jmotta/ref=jmotta>
> !
>
>
>
> On Mon, Jul 4, 2011 at 11:54 AM, Thiago <thiagorossi...@gmail.com> wrote:
>
>> Hi.
>>
>> I'm using Google App Engine and I really liked it. It was a bit
>> difficult in the beginning because there are more documentation for
>> Python and I only know Java but now I think I'm going well.
>>
>> I'm using JDO and I understand that do add a child to a one to many
>> relationship I need to do this:
>>
>> User user = pm.getObjectById(User.class.getName(), "thiago");
>> LoginHistory loginHistory = new LoginHistory(now);
>> loginHistory.setKey(user.getKey().getChild(LoginHistory.class.getName(),
>> now.getTime());
>> user.getLoginHistory(loginHistory);
>> pm.close();
>>
>> I loginHostory has to have User as the parent, so User("thiago")/
>> LoginHistory([time]). I can't do makePersistent(myChild) because it
>> won't appear in the collection or anywhere with user, so I don't know
>> how JDO makes the link with the collection because I can't see in the
>> Datastore Viewer.
>>
>> But my real question is: I have an entity and the collection is really
>> big, like user.getLoginHistory(), and I think after a lot of logins it
>> will be wrong to retrieve this collection just to add a new child.
>> Isn't there any way to create a child in a collection without using
>> the parent? Something like makePersistent(newChild) and newChild have
>> the key like I said? Or how can I do this using Datastore (low level
>> API)? I can't see the property with the collection in the Datastore
>> viewer.
>>
>> Thank you very much.
>>
>> PS: Sorry for my English, I'm brazilian.
>>
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