Drill up broken in a tree based on a union

Question

Situation: there are six real root rows in the table and they have 0 in the parent id, so I added a single root to the tree select statement:
UNION
SELECT 0 id, NULL pid, 'Root' name, null link, null a1, null a2 FROM DUAL
The whole tree displays ok starting from "Root" if I set the tree root item value to 0. The nodes have drill down links that make the selected node the new root. When you do that, the new root shows an "up" link that lets you drill up again, except that the six actual root nodes never show it so you can't drill back up to "Root" after drilling down (or setting the initial root item value to other than 0). Questions:
What could be going wrong?
Is there any even a little better documentation on trees than in User's Guide "Creating Trees"?
What exactly is the logic determining whether the drill up link is shown or not? It seemed to be: if the current root has any parents in the select stmt result set, show it. Not in this case though.
Is there a way to see the actual select statement that was executed to generate the tree?

Answer 1

Hi,
I don't know why this is, but the problem is because you are using 0 as the pseudo root ID. I've just been trying this out and found that if I changed this to 1, then the (up) link appears ok. It is possible that null values are being treated as zeros because most ID values will be greater than 0.
For simplicity, I also created a view over my EMP data as:
CREATE OR REPLACE FORCE VIEW "TREEDATA"
(ID, PID, NAME)
AS
SELECT 1 ID,
       NULL PID,
       'Root' NAME
FROM DUAL
UNION
select EMPNO ID,
       CASE WHEN MGR IS NULL THEN 1 ELSE MGR END PID,
       ENAME NAME
from EMPand the tree was then defined as:
select ID,
       PID,
       NAME,
       'f?p='||:APP_ID||':125:'||:SESSION||'::NO::P125_TREE_ROOT:'||ID LINK,
       null A1,
       null A2
from TREEDATA
ORDER BY NAMEThe default on the P125_TREE_ROOT item was set to 1 (Only when current value in session state is null).
I have not seen any other documentation - I'm sure it's out there somewhere, perhaps in the upcoming Pro Oracle Application Express book or a blog.
Andy