[appengine-java] Re: Possible to Add Child to Owned One to Many Relationship Without Loading All Children?
You hit the nail on the head. As far as I know there is nothing like sequence in Google App Engine. Either you need to have another entity with a counter and increase it in transactional way. Or you can use memcache. http://code.google.com/intl/pl/appengine/docs/java/javadoc/com/google/appengine/api/memcache/MemcacheService.html There is a method: java.lang.Long increment(java.lang.Object key, long delta) Atomically fetches, increments, and stores a given integral value. --- Pay attention to atomically. May be this can be used for generating sequential and avoid bottleneck in the case of datastore entity and additional transaction. But because of the risk of memcache expiring this method needs some more elaboration. --~--~-~--~~~---~--~~ You received this message because you are subscribed to the Google Groups Google App Engine for Java group. To post to this group, send email to google-appengine-java@googlegroups.com To unsubscribe from this group, send email to google-appengine-java+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/google-appengine-java?hl=en -~--~~~~--~~--~--~---
[appengine-java] Re: Possible to Add Child to Owned One to Many Relationship Without Loading All Children?
Maybe what you are looking for is DatastoreService.allocateIds(). On Oct 21, 9:35 am, leszek leszek.ptokar...@gmail.com wrote: You hit the nail on the head. As far as I know there is nothing like sequence in Google App Engine. Either you need to have another entity with a counter and increase it in transactional way. Or you can use memcache. http://code.google.com/intl/pl/appengine/docs/java/javadoc/com/google... There is a method: java.lang.Long increment(java.lang.Object key, long delta) Atomically fetches, increments, and stores a given integral value. --- Pay attention to atomically. May be this can be used for generating sequential and avoid bottleneck in the case of datastore entity and additional transaction. But because of the risk of memcache expiring this method needs some more elaboration. --~--~-~--~~~---~--~~ You received this message because you are subscribed to the Google Groups Google App Engine for Java group. To post to this group, send email to google-appengine-java@googlegroups.com To unsubscribe from this group, send email to google-appengine-java+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/google-appengine-java?hl=en -~--~~~~--~~--~--~---
[appengine-java] Re: Possible to Add Child to Owned One to Many Relationship Without Loading All Children?
Thanks Nacho. I asked the same question in google appengine chat irc and got the same answer. Will have to use the allocate id feature in low level api. Len On Oct 21, 7:41 am, Nacho Coloma icol...@gmail.com wrote: Maybe what you are looking for is DatastoreService.allocateIds(). On Oct 21, 9:35 am, leszek leszek.ptokar...@gmail.com wrote: You hit the nail on the head. As far as I know there is nothing like sequence in Google App Engine. Either you need to have another entity with a counter and increase it in transactional way. Or you can use memcache. http://code.google.com/intl/pl/appengine/docs/java/javadoc/com/google... There is a method: java.lang.Long increment(java.lang.Object key, long delta) Atomically fetches, increments, and stores a given integral value. --- Pay attention to atomically. May be this can be used for generating sequential and avoid bottleneck in the case of datastore entity and additional transaction. But because of the risk of memcache expiring this method needs some more elaboration.- Hide quoted text - - Show quoted text - --~--~-~--~~~---~--~~ You received this message because you are subscribed to the Google Groups Google App Engine for Java group. To post to this group, send email to google-appengine-java@googlegroups.com To unsubscribe from this group, send email to google-appengine-java+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/google-appengine-java?hl=en -~--~~~~--~~--~--~---
[appengine-java] Re: Possible to Add Child to Owned One to Many Relationship Without Loading All Children?
I'm afraid that it is not possible. But if the purpose of your relationship is only to manage child class in a transactional way you don't need to keep them as a part of child relationship. Simply use Key type and set 'parent' part of the child' key being the same and you can manage them in the same transaction. --~--~-~--~~~---~--~~ You received this message because you are subscribed to the Google Groups Google App Engine for Java group. To post to this group, send email to google-appengine-java@googlegroups.com To unsubscribe from this group, send email to google-appengine-java+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/google-appengine-java?hl=en -~--~~~~--~~--~--~---
[appengine-java] Re: Possible to Add Child to Owned One to Many Relationship Without Loading All Children?
Thanks leszek. We are going do what you suggest (the JPA
equivalent).
In order to generate the unique part of the child's key, I'm wondering
if there is a way to use sequence in JPA. In JDO, I think you can do
something like:
Sequence seq = pm.getSequence(child.sequence);
long id = seq.nextValue();
Does anyone know if there is an equivalent to this in JPA, i.e. to
get direct access to a sequence?
Thanks,
Len
On Oct 20, 4:04 am, leszek leszek.ptokar...@gmail.com wrote:
Look at the code snippet below:
// entity class
@PersistenceCapable(identityType = IdentityType.APPLICATION)
public class ChildEnt {
@PrimaryKey
@Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY)
// �...@extension(vendorName=datanucleus, key=gae.encoded-
pk,value=true)
private Key encodedKey;
private String info;
public Key getEncodedKey() {
return encodedKey;
}
public void setEncodedKey(Key encodedKey) {
this.encodedKey = encodedKey;
}
public String getInfo() {
return info;
}
public void setInfo(String info) {
this.info = info;
}
}
// transaction code
PersistenceManager pm = PMF.get().getPersistenceManager();
Key parkey = KeyFactory.createKey(Parent,P01);
ChildEnt e1 = new ChildEnt();
ChildEnt e2 = new ChildEnt();
ChildEnt e3 = new ChildEnt();
Key k1 = KeyFactory.createKey(parkey,ChildEnt.class.getSimpleName(),
1);
Key k2 = KeyFactory.createKey(parkey,ChildEnt.class.getSimpleName(),
2);
Key k3 = KeyFactory.createKey(parkey,ChildEnt.class.getSimpleName(),
3);
e1.setEncodedKey(k1);
e1.setInfo(info1);
e2.setEncodedKey(k2);
e2.setInfo(info2);
e3.setEncodedKey(k3);
e3.setInfo(info3);
pm.currentTransaction().begin();
pm.makePersistent(e1);
pm.makePersistent(e2);
pm.makePersistent(e3);
pm.currentTransaction().commit();
pm.close();
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