You can use DatastoreService.allocateIds() to get a range of unique
keys that you can then assign to the children. The kind name can be
any old String - not just an existing kind. This method does not
guarantee the ids will be sequential but they will be unique.
If you really need sequential ids you can use memcache's atomic
increment method. If the value is not found in memcache you can do a
query to find the maximum sequence number in the datastore and use the
memcache increment method that allows you to specify an initial
missing value atomically.
John
On 30 Sep 2010, at 17:28, Fred wrote:
Hi Group,
I know key ids are only unique across entity groups so what GAE + JDO
gives me is:
/Parent[1]/Child[1]
/Parent[1]/Child[2]
/Parent[1]/Child[3]
/Parent[2]/Child[1]
/Parent[2]/Child[2]
/Parent[3]/Child[1]
etc.
What I need to achieve (aka implement) is a way to assign keys in the
following fashion:
/Parent[1]/Child[1]
/Parent[1]/Child[2]
/Parent[1]/Child[3]
/Parent[2]/Child[4]
/Parent[2]/Child[5]
/Parent[3]/Child[6]
etc... so child ids are in sequence across entity groups (or at least
unique). Does anyone have experience with this or any thoughts on how
to go about it in a secure fashion?
I can't seem to come up with a secure way of doing this, but don't
want to give up on it because it would give my use case a lot of
querying power.
Hope someone can help.
Thanks in advance,
Fred
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