Advanced: How to traverse a tree representation in PL/SQL (procedure)?

Question

I am looking to write a method that will create a collection of records, each of which represents a node in a tree.
TYPE t_all_folders IS TABLE OF get_all_folders%ROWTYPE INDEX BY PLS_INTEGER;
v_all_folders t_all_folders;
so first need help in figuring out what the cursor 'get_all_folders' would look like
I have a folder structure represented in a database that is used basically to show visually
(with a front end app) a folder structure (much like a folder structure in a file system).
So each row has an entry in the 'folders' table like do:
table folder:
     column           column
     folder_id          name
     1                    folder1               <= say this is a root folder
     2                    folder2               <= say this is a root folder
     3                    folder3               <= say this is a root folder
     4                    folder1a          <= all below are child folders..
     5                    folder1b
     6                    folder1c
     7                    folder1aa
     8                    folder1ab
     There is nothing in this table that indicates a hiearchy.
The hiearchy is represented by another single table with two columns
(I cannot change this, it is what it is)
There is no left node or right node (not like a tree), just imagine sub folders.
table: parent_child
     column          column
     parent_id     child_id
such that visually when the tables are queried and the UI uses a folder icon to
represent each row:
it would look like this:
     folder1                              1
          - folder1a                         2
               -folder1aa                    3
               - folder1ab                    4
          - folder1b                         5
               - folder1ba                    6
               - folder1bb                    7
          - folder1c                         8
     folder2                              9
     folder3                              10
I am attempting to create a query that will add to a collection folder records in the
order above (1..10)
In other words traverse the tree depth first going from:
          folder1 -> folder1a -> folder1aa -> folder1ab ->(back out to next level) folder1b -> folder1ba -> folder1bb -> folder1c
          then add folder2 (and traverse down that hiearch if needed)
          and then add folder3 to the colleciton and traverse down that hiearchy if there is one
          and continue adn so on.
          The requirement is to have them added to the collection in that order and when I iterate through the collection,
          they would of course need to be pulled out in that order (so use vararray with a counter to iterate through
          after the collection has been created.
After the collection has been created, I have to iterate in that specific order to create records in another table where there is a column that requires an integer value that is the 1... order they come out of the collection
and then have to iterate again and do something else in that order (and then other things - all the while needing in that order).
Edited by: user12200443 on Nov 19, 2012 11:49 AM

Answer 1

awesome, thanks for the help.
put this in 'schema.sql' and run to create a reference schema and data for the example
drop sequence seq_folders;
CREATE SEQUENCE seq_folders
INCREMENT BY 1
MINVALUE 1
START WITH 1
CACHE 1000;
drop table folders;
create table folders (
     folder_id number not null,
     name varchar2(20) not null
drop table parent_child;
create table parent_child (
     parent_id number not null,
     child_id number not null);
-- creation order (in order to have parent)
-- folder1
-- folder2
-- folder3
-- folder1a
-- folder1b
-- folder1c
-- folder1aa
-- folder1ab
-- folder1ac
-- folder1aaa
-- folder1aba
-- folder1aab
-- folder1abb
-- folder1aac
-- folder1abc
-- Visual hiearchy
-- folder1                              1
--      folder1a                         2
--           folder1aa               3
--                folder1aaa          4
--                folder1aab          5
--                folder1aac          6
--           folder1ab               7
--                folder1aba          8
--                folder1abb          9
--           folder1ac               10
--      folder1b                         11
--      folder1c                         12
-- folder2                              13
-- folder3                              14
--- insert folders
insert into folders(folder_id, name) values(seq_folders.nextval, 'folder1');
insert into folders(folder_id, name) values(seq_folders.nextval, 'folder2');
insert into folders(folder_id, name) values(seq_folders.nextval, 'folder3');
insert into folders(folder_id, name) values(seq_folders.nextval, 'folder1a');
insert into folders(folder_id, name) values(seq_folders.nextval, 'folder1b');
insert into folders(folder_id, name) values(seq_folders.nextval, 'folder1c');
insert into folders(folder_id, name) values(seq_folders.nextval, 'folder1aa');
insert into folders(folder_id, name) values(seq_folders.nextval, 'folder1ab');
insert into folders(folder_id, name) values(seq_folders.nextval, 'folder1ac');
insert into folders(folder_id, name) values(seq_folders.nextval, 'folder1aaa');
insert into folders(folder_id, name) values(seq_folders.nextval, 'folder1aba');
insert into folders(folder_id, name) values(seq_folders.nextval, 'folder1aab');
insert into folders(folder_id, name) values(seq_folders.nextval, 'folder1abb');
insert into folders(folder_id, name) values(seq_folders.nextval, 'folder1aac');
insert into folders(folder_id, name) values(seq_folders.nextval, 'folder1abc');
commit;
-- setup hiearchy
insert into parent_child(parent_id, child_id) values (0, (select folder_id from folders where name = 'folder1'));
insert into parent_child(parent_id, child_id) values (0, (select folder_id from folders where name = 'folder2'));
insert into parent_child(parent_id, child_id) values (0, (select folder_id from folders where name = 'folder3'));
-- 1a,1b,1c
insert into parent_child(parent_id, child_id) values ((select folder_id from folders where name ='folder1'), (select folder_id from folders where name = 'folder1a'));
insert into parent_child(parent_id, child_id) values ((select folder_id from folders where name ='folder1'), (select folder_id from folders where name = 'folder1b'));
insert into parent_child(parent_id, child_id) values ((select folder_id from folders where name ='folder1'), (select folder_id from folders where name = 'folder1c'));
-- aa,ab,ac
insert into parent_child(parent_id, child_id) values ((select folder_id from folders where name ='folder1a'), (select folder_id from folders where name = 'folder1aa'));
insert into parent_child(parent_id, child_id) values ((select folder_id from folders where name ='folder1a'), (select folder_id from folders where name = 'folder1ab'));
insert into parent_child(parent_id, child_id) values ((select folder_id from folders where name ='folder1a'), (select folder_id from folders where name = 'folder1ac'));
-- aaa,aba,aab
insert into parent_child(parent_id, child_id) values ((select folder_id from folders where name ='folder1aa'), (select folder_id from folders where name = 'folder1aaa'));
insert into parent_child(parent_id, child_id) values ((select folder_id from folders where name ='folder1aa'), (select folder_id from folders where name = 'folder1aab'));
insert into parent_child(parent_id, child_id) values ((select folder_id from folders where name ='folder1aa'), (select folder_id from folders where name = 'folder1aac'));
-- aba,abb,abc
insert into parent_child(parent_id, child_id) values ((select folder_id from folders where name ='folder1ab'), (select folder_id from folders where name = 'folder1aba'));
insert into parent_child(parent_id, child_id) values ((select folder_id from folders where name ='folder1ab'), (select folder_id from folders where name = 'folder1abb'));
insert into parent_child(parent_id, child_id) values ((select folder_id from folders where name ='folder1ab'), (select folder_id from folders where name = 'folder1abc'));
commit;
then run this to get the error message
WITH joined_data     AS
     SELECT     f.folder_id,     f.name,     pc.parent_id
     FROM     folders     f
     JOIN     parent_child     pc ON pc.child_id = f.folder_id
SELECT     j.*,     ROWNUM     
AS r_num
FROM joined_data     j
START WITH     parent_id =0
CONNECT BY     parent_id= PRIOR child_id
ORDER SIBLINGS BY     name;
thanks for the help, hopefully I can find a way to read the rows/record into a data structure (does not have to be a single sql statement - can be anything I can do in PL/SQL.
Edited by: user12200443 on Nov 19, 2012 5:55 PM