Thanks for the reply! I use KeyFactory extensively in my code and I've read almost all the blog posts on that blog.
It's not a question of yes or no but just for a better solution:-) On May 6, 10:44 pm, Chau Huynh <cmhu...@gmail.com> wrote: > Have you tried with > KeyFactory?http://code.google.com/appengine/docs/java/javadoc/com/google/appengi... > > In this post Max Ross of Google guided how to query with Key, may it help > you..http://gae-java-persistence.blogspot.com/2010/01/querying-with-key-pa... > > > > On Thu, May 6, 2010 at 9:10 PM, Kenyth <ken...@gmail.com> wrote: > > I was partly wrong in the previous post, and finding what was wrong > > also leads me to the answer to the question asked in the previous > > post. > > > Even using the encoded String key in conjunction with annotated > > "gae.pk-name" or "gae.pk-id", it is still impossible to make a query > > with only the key name/id. Below is error messages when you try to do > > so: > > > "<key name/id> is a sub-component of the primary key. The datastore > > does not support filtering or sorting by primary key components, only > > the entire primary key" > > > You have to use the complete primary key to do the query, not part of > > it. So in this case you either make your key name/id the primary key > > or just use the Key instance as the primary key. > > > It turns out using the encoded String key in conjunction with > > annotated "gae.pk-name" or "gae.pk-id" only provide you with shortcuts > > to access the key name/id, no other benefits. > > > On May 6, 7:30 pm, Kenyth <ken...@gmail.com> wrote: > > > Is there any way that key name (or pk-name), key id (or pk-id), or > > > even parent key (or parent-key) can be used in a query regardless of > > > JPQL or JDQL. I know in the Python edition it's possible (correct me > > > if I'm wrong). > > > > If there's no way to use this kind query, then the power of key name > > > or id (obviously from the GAE doc you can always benefit from a > > > annotated parent key) would be very limited *except that you always > > > use encoded string key in conjunction with annotated "gae.pk-name" or > > > "gae.pk-id"*. > > > > // More to read if you would like to... > > > From my limited experience with GAE/J, in a normal app key name/id is > > > a very simple but powerful way to achieve uniqueness. For example, > > > when you have multiple concurrent requests to create a root entity, in > > > each request handler you would first check if it exists and then > > > decide to create a new one or use the existing one. Without using key > > > name/id it's very hard, if possible, to ensure the uniqueness. > > > > Because as far as I know in this case, the global unique key generated > > > by the datastore is used to decide the transaction commit will succeed > > > or fail. For the root entities, given the same entity kind and the > > > same key name/id, the generated key instance will always be the same, > > > so you can just let the transaction fail or try it again to rewrite > > > it, but using other fields (say, "name" of a value) than key name/id, > > > in all concurrent transactions a new entity will be created and the > > > transaction commit will succeed since the generated key instance will > > > always be different from each other. > > > > If in this case I would like to always use key name/id I roughly have > > > three choices: > > > 1. use Long key or unencoded String key for the entity kind, but the > > > downside of this is you can't make this entity kind be child of any > > > entity kind any more according to the official GAE doc; > > > 2. use Key instance, but the downside is about this question asked in > > > this post: you may use key name/id to make a query; > > > 3. use encoded String key in conjunction with annotated "gae.pk-name" > > > or "gae.pk-id", and the only downside is you have always to use > > > KeyFactory to convert the encoded string to a Key instance when you > > > need one (e.g., to establish an unowned relationship) > > > > Last, what's described above seems also be true for entities with a > > > parent. I'm not sure. > > > > -- > > > 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-j...@googlegroups.com. > > > To unsubscribe from this group, send email to > > google-appengine-java+unsubscr...@googlegroups.com<google-appengine-java%2bunsubscr...@googlegroups.com> > > . > > > For more options, visit this group athttp:// > > groups.google.com/group/google-appengine-java?hl=en. > > > -- > > 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-j...@googlegroups.com. > > To unsubscribe from this group, send email to > > google-appengine-java+unsubscr...@googlegroups.com<google-appengine-java%2bunsubscr...@googlegroups.com> > > . > > For more options, visit this group at > >http://groups.google.com/group/google-appengine-java?hl=en. > > -- > 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-j...@googlegroups.com. > To unsubscribe from this group, send email to > google-appengine-java+unsubscr...@googlegroups.com. > For more options, visit this group > athttp://groups.google.com/group/google-appengine-java?hl=en. -- You received this message because you are subscribed to the Google Groups "Google App Engine for Java" group. 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