Tree mapping

Question

Hi.
I'm trying to implement tree-like structure using Kodo. Each tree element
has a reference to it's parent (save root node which obviously has null
parent node). Everything seems to run fine except the fact, that when
fetching any tree node all nodes up to root nodes are selected from the
database. That seems to be quite logical - I want to obtain some node along
with it's parent node (it that exists) - so I set "parent node field"
fetchgroup to current fetchgroups list, fetch data from the database, but
since parent node and child node are the same class, "parent node field"
fetchgroup is also valid for parent node. That results in fetching parent's
parent node - but since it's still same class also it's parent is fetched..
and so on. What should I do to make Kodo working the way I want it to? :)
Regards,
Pawel

Answer 1

Hi
I think the structure is the other way round:
Node {
Node parent;
String someData;
Now if you add "parent" to your default-fetch-group, you will load all
objects up to the root, because fetch-groups are recursive.
I suggest avoiding the default-fetch-group for parent completely, JDO will
load the information from the parent when you actually need it.
Sven Erik Knop
"Keiron McCammon" <[email protected]> wrote in message
news:bumint$ms4$[email protected]..
Hi Pawel,
I may have missed what you want but it sounds like you have a singleclass:
Node {
Node parent;
Set children; /* Which contains Node */
Now I'm not sure quite what behavior you desire.
If you don't want to fetch a Node's parent and so forth upto the root then
you need to ensure the 'parent' field isn't in any fetch group (default or
otherwise)?
Cheers
- Keiron