How to populate TABLE OF RECORDS with rows of 2 levels parent-child - oracle

Question

I have a table with rows describing a tree, columns are:
(column child_num is unique and used as primary key)
TABLE items_tree (
child_num number,
parent_ref varchar2(10),
child_ref varchar2(10)
);
TYPE item_rec_type IS RECORD (
item_id NUMBER,
spaces_number NUMBER,
parent_ref VARCHAR2(10),
child_ref VARCHAR2(10)
);
TYPE tree_table_type IS TABLE OF item_rec_type%ROWTYPE
INDEX BY BINARY_INTEGER;
table_tree tree_table_type; -- table of all items
Example data for table items_tree (values of child_num are not relevant):
parent_ref child_ref
---------------------------
null Abraham
Abraham Isaac
Abraham Ishmael
Isaac Jakob
Jakob Yehuda
Jakob Josef
Jakob Benjamin
Yehuda David
Josef Efraim
Josef Menashe
David Solomon
Solomon Isaiah
Isaiah Jeremiah
I need to populate table_tree records from items_tree table. To do so, I am using a package, the item_rec_type, tree_table_type, table_tree are defined in it and two procedures: print_tree which retrieves the ROOT items of the tree, starts the process and prints the tree from table_tree. Second procedure get_items_by_parent_recursively is recursive procedure that retrieves all the items or a parent item, e.g. calling get_items_by_parent_recursively('Abraham') will add Isaac and Ishmael to table_tree.
The cursor is declared in the package body:
CURSOR get_children_cur(c_parent in varchar2(10))
IS
SELECT parent_ref, child_ref
FROM items_tree
WHERE parent_ref = c_parent
ORDER BY 1, 2;
The code in get_items_by_parent_recursively that retrieves the items for the parent:
procedure get_items_by_parent_recursively(p_parent in VARCHAR2(10), p_spaces_number in NUMBER )
AS
l_spaces_number NUMBER := 0;
l_child VHARCHAR2(10);
l_parent VHARCHAR2(10);
BEGIN
l_spaces_number := p_spaces_number + 3;
OPEN get_children_cur(p_parent);
LOOP
FETCH get_children_cur INTO l_parent, l_child;
EXIT WHEN get_children_cur%NOTFOUND;
IF (l_child is not null) THEN
v_row_number := v_row_number + 1;
tree_table(v_row_number).row_num := v_row_number;
tree_table(v_row_number).spaces_number := l_spaces_number;
tree_table(v_row_number).parent_ref := l_parent;
tree_table(v_row_number).child_ref := l_child;
-- Calling procedure recursively
get_items_by_parent_recursively( l_child, l_spaces_number );
END IF;
END LOOP;
CLOSE get_children_cur;
EXCEPTION
WHEN CURSOR_ALREADY_OPEN THEN
DBMS_OUTPUT.put_line(' Exception -- CURSOR_ALREADY_OPEN');
WHEN INVALID_CURSOR THEN
DBMS_OUTPUT.put_line(' Exception -- INVALID_CURSOR');
WHEN INVALID_NUMBER THEN
DBMS_OUTPUT.put_line(' Exception -- INVALID_NUMBER');
WHEN NO_DATA_FOUND THEN
DBMS_OUTPUT.put_line(' Exception -- NO_DATA_FOUND');
WHEN PROGRAM_ERROR THEN
DBMS_OUTPUT.put_line(' Exception -- PROGRAM_ERROR');
WHEN ROWTYPE_MISMATCH THEN
DBMS_OUTPUT.put_line(' Exception -- ROWTYPE_MISMATCH');
WHEN STORAGE_ERROR THEN
DBMS_OUTPUT.put_line(' Exception -- STORAGE_ERROR');
WHEN TOO_MANY_ROWS THEN
DBMS_OUTPUT.put_line(' Exception -- TOO_MANY_ROWS');
WHEN VALUE_ERROR THEN
DBMS_OUTPUT.put_line(' Exception -- VALUE_ERROR');
END get_items_by_parent_recursively;
Running this procedure I am getting the exception: CURSOR_ALREADY_OPEN.
I have searched for a reply, but none came close to what I need. I will appreciate any ideas.
I will try to make the cursor get_children_cur part of the recursive procedure.

Answer 1

As #vmachan said, you need to move the cursor definition into the procedure. While you have it in the package specification or body, but outside the procedure, there is one instance of it which is global to the session. Each call to your procedure attempts to open the same cursor; the initial call from print_tree succeeds, and your table is populated with 'Abraham'; but then the recursive call tries to re-open it and gets the CURSOR_ALREADY_OPEN exception, and stops.
Moving the cursor into the procedure means each call/iteration has its own independent copy. Cleaning up naming and various other issues, this then works:
procedure get_items_by_parent(p_parent in VARCHAR2, p_spaces_number in NUMBER)
AS
l_spaces_number NUMBER := 0;
l_child VARCHAR2(10);
l_parent VARCHAR2(10);
CURSOR get_children_cur(p_parent in varchar2) IS
SELECT parent_item, child_item
from items_tree
where parent_item = p_parent
or (p_parent is null and parent_item is null);
BEGIN
l_spaces_number := p_spaces_number + 3;
OPEN get_children_cur(p_parent);
LOOP
FETCH get_children_cur INTO l_parent, l_child;
EXIT WHEN get_children_cur%NOTFOUND;
IF (l_child is not null) THEN
v_row_number := v_row_number + 1;
table_tree(v_row_number).item_id := v_row_number;
table_tree(v_row_number).spaces_number := l_spaces_number;
table_tree(v_row_number).parent_item_ref := l_parent;
table_tree(v_row_number).item_ref := l_child;
-- Calling procedure recursively
get_items_by_parent( l_child, l_spaces_number );
END IF;
END LOOP;
CLOSE get_children_cur;
EXCEPTION
WHEN CURSOR_ALREADY_OPEN THEN
DBMS_OUTPUT.put_line(' Exception -- CURSOR_ALREADY_OPEN');
WHEN INVALID_CURSOR THEN
DBMS_OUTPUT.put_line(' Exception -- INVALID_CURSOR');
WHEN INVALID_NUMBER THEN
DBMS_OUTPUT.put_line(' Exception -- INVALID_NUMBER');
WHEN NO_DATA_FOUND THEN
DBMS_OUTPUT.put_line(' Exception -- NO_DATA_FOUND');
WHEN PROGRAM_ERROR THEN
DBMS_OUTPUT.put_line(' Exception -- PROGRAM_ERROR');
WHEN ROWTYPE_MISMATCH THEN
DBMS_OUTPUT.put_line(' Exception -- ROWTYPE_MISMATCH');
WHEN STORAGE_ERROR THEN
DBMS_OUTPUT.put_line(' Exception -- STORAGE_ERROR');
WHEN TOO_MANY_ROWS THEN
DBMS_OUTPUT.put_line(' Exception -- TOO_MANY_ROWS');
WHEN VALUE_ERROR THEN
DBMS_OUTPUT.put_line(' Exception -- VALUE_ERROR');
END get_items_by_parent;
Inventing a print_tree based on what you describe:
procedure print_tree is
begin
get_items_by_parent(null, 0);
for i in 1..table_tree.count loop
dbms_output.put_line(to_char(table_tree(i).item_id, '99999') || ' '
|| lpad(' ', table_tree(i).spaces_number, ' ')
|| table_tree(i).item_ref);
end loop;
end print_tree;
... calling that now works, and produces 13 indented records:
1 Abraham
2 Isaac
3 Jakob
4 Yehuda
5 David
6 Solomon
7 Isaiah
8 Jeremiah
9 Josef
10 Efraim
11 Menashe
12 Benjamin
13 Ishmael
As #XING said, you can get the same result more simply with a different for of cursor loop:
procedure get_items_by_parent(p_parent in VARCHAR2, p_spaces_number in NUMBER)
AS
l_spaces_number NUMBER := 0;
CURSOR get_children_cur(p_parent in varchar2) IS
SELECT parent_item, child_item
from items_tree
where child_item is not null
and (parent_item = p_parent
or (p_parent is null and parent_item is null));
BEGIN
l_spaces_number := p_spaces_number + 3;
FOR r IN get_children_cur(p_parent)
LOOP
v_row_number := v_row_number + 1;
table_tree(v_row_number).item_id := v_row_number;
table_tree(v_row_number).spaces_number := l_spaces_number;
table_tree(v_row_number).parent_item_ref := r.parent_item;
table_tree(v_row_number).item_ref := r.child_item;
-- Calling procedure recursively
get_items_by_parent( r.child_item, l_spaces_number );
END LOOP;
END get_items_by_parent;
or even:
procedure get_items_by_parent(p_parent in VARCHAR2, p_spaces_number in NUMBER)
AS
BEGIN
FOR r IN (
SELECT parent_item, child_item
from items_tree
where child_item is not null
and (parent_item = p_parent
or (p_parent is null and parent_item is null)))
LOOP
v_row_number := v_row_number + 1;
table_tree(v_row_number).item_id := v_row_number;
table_tree(v_row_number).spaces_number := p_spaces_number + 3;
table_tree(v_row_number).parent_item_ref := r.parent_item;
table_tree(v_row_number).item_ref := r.child_item;
-- Calling procedure recursively
get_items_by_parent( r.child_item, p_spaces_number + 3 );
END LOOP;
END get_items_by_parent;
Of course, you don't need to use PL/SQL or a table at all, you can use a hierarchical query:
select rownum, lpad(' ', level * 3, ' ') || child_item as item
from items_tree
start with parent_item is null
connect by parent_item = prior child_item
order siblings by child_num;
ROWNUM ITEM
---------- --------------------------------------------------
1 Abraham
2 Isaac
3 Jakob
4 Yehuda
5 David
6 Solomon
7 Isaiah
8 Jeremiah
9 Josef
10 Efraim
11 Menashe
12 Benjamin
13 Ishmael
but presumably this is a PL/SQL exercise. If you aren't required to use a recursive procedure you could still populate your table from a similar query, using bulk collect.