Parent Child In Same Table Management

Question

I have a simple entity (Process) which has ID and Name.
It also has Parent property which reference the parent Process of this one.
When the user ask to delete a process, I have to disconnect its children from it, otherwise I'll have a reference integrity violation, and the logic of the application permit to delete a process in the middle of hierarchy.
The question is where is it best to put the code that will handle it?
In a session bean managing the processes, the bad thing is that there are other places that delete processes. so the logic will be have to be duplicated.
Maybe in an entity listener, the problem is how to get hold of an EntityManager there to update the child processes when a parent process is deleted?
Thank you,
Ido.

Answer 1

Hi,
In a CONNECT BY query, related rows will always come together. That is, if row r p has children, then the row immediately after p will be one of p's children, and all of the descendants of p will come before any row that is not a descendant of p.
An ORDER BY clause will cancel the above, but an ORDER SIBLINGS BY clause will keep to the rules above.
For example:
SELECT     *
FROM     t1
START WITH        col1  NOT IN ( SELECT  col2
                                           FROM        t1
                         WHERE   col2        IS NOT NULL
CONNECT BY         col1  = PRIOR col2
ORDER SIBLINGS BY  id               -- Optional
;It just so happens that the rows appear in order by id. It might have been better if you had chosen ids that did not show the correct order.
The tricky part of the CONNECT BY query above is choosing the START WITH set. There's noting in each row by itself that tells if a row is a root; you have to do a sub-query to find all the children, and START WITH a row if it is not on that list.