Why does this get-or-create function never seem to insert? - oracle

Question

I'm writing a function for batch-importing data into our org-chart. It seems to work fine for retrieving entries that already exists, but when an entry does not already exist, and it's supposed to insert, commit, and return the result of a re-attempt (so as to get the auto-generated ID), it always returns NULL.
I'm sure I'm doing something wrong here, but what? Help appreciated.
Note: there's a before-insert trigger that fills in DEPT_ID if it's not specified. Works fine if the insert statement is executed by hand.
CREATE TABLE DEPTS
(
"DEPT_ID" VARCHAR2(10 BYTE),
"HEADER_ID" VARCHAR2(10 BYTE),
"COMMENTS" VARCHAR2(100 BYTE),
"CATEGORY" VARCHAR2(2 BYTE)
);
CREATE OR REPLACE FUNCTION get_or_make_unit(
, in_cat VARCHAR2
, in_cmt VARCHAR2
, in_hdr VARCHAR2 DEFAULT NULL
) RETURN VARCHAR2 AS
unit_id VARCHAR2(10);
BEGIN
unit_id := NULL;
IF in_hdr IS NULL THEN
SELECT dept_id
INTO unit_id
FROM depts unit
WHERE unit.category = in_cat
AND unit.comments = in_cmt
AND unit.header_id IS NULL;
ELSE
SELECT dept_id
INTO unit_id
FROM depts unit
WHERE unit.category = in_cat
AND unit.comments = in_cmt
AND unit.header_id = in_hdr;
END IF;
IF unit_id IS NULL THEN
DBMS_OUTPUT.PUT_LINE('Inserting!');
INSERT INTO depts (
header_id
, comments
, category
) VALUES (
in_hdr
, in_cmt
, in_cat);
COMMIT;
unit_id := get_or_make_unit(in_cat, in_cmt, in_hdr);
RETURN unit_id;
ELSE
DBMS_OUTPUT.PUT_LINE('Not inserting!');
RETURN unit_id;
END IF;
END get_or_make_unit;
And the trigger:
CREATE OR REPLACE TRIGGER HRD.DEPTS_BIR
BEFORE INSERT
ON HRD.DEPTS
FOR EACH ROW
DECLARE
JML NUMBER;
BEGIN
SELECT SEQ_DEPT_ID.NEXTVAL INTO JML FROM DUAL;
:NEW.DEPT_ID:='D'||to_char(JML);
END DEPTS_BIR;
Examples
This works:
INSERT INTO depts (
header_id
, comments
, category
) VALUES (
'D532'
, 'ACCOUNTING'
, '2');
COMMIT;
SELECT get_or_make_unit('2', 'ACCOUNTING', 'D532') FROM DUAL;
=> 'D533'
This does not:
SELECT get_or_make_unit('2', 'NEW DEPT', 'D532') FROM DUAL;
=> NULL

Answer 1

Instead of:
INSERT INTO depts (
header_id
, comments
, category
) VALUES (
in_hdr
, in_cmt
, in_cat);
COMMIT;
unit_id := get_or_make_unit(in_cat, in_cmt, in_hdr);
use RETURNING INTO:
INSERT INTO depts (
header_id
, comments
, category
) VALUES (
in_hdr
, in_cmt
, in_cat) RETURNING dept_id INTO unit_id;
COMMIT;
I think recursive call in not the best approach, but if you are strict of using it, then please post definition of mentioned before-insert trigger.
UPDATE: You cannot call functions containing DML operations from SQL statement. Please see this answer for details. Example of correct call:
DECLARE
unit_id varchar2(32);
BEGIN
unit_id := get_or_make_unit('2', 'NEW DEPT', 'D532');
dbms_output.put_line(unit_id);
END;
UPDATE2: Also you need to catch NO_DATA_FOUND exception that is raised when you call your function with not existent combination. Below is example:
CREATE OR REPLACE FUNCTION get_or_make_unit(in_cat VARCHAR2,
in_cmt VARCHAR2,
in_hdr VARCHAR2 DEFAULT NULL)
RETURN VARCHAR2 AS
unit_id VARCHAR2(10);
BEGIN
unit_id := NULL;
IF in_hdr IS NULL THEN
SELECT dept_id
INTO unit_id
FROM depts unit
WHERE unit.category = in_cat
AND unit.comments = in_cmt
AND unit.header_id IS NULL;
ELSE
SELECT dept_id
INTO unit_id
FROM depts unit
WHERE unit.category = in_cat
AND unit.comments = in_cmt
AND unit.header_id = in_hdr;
END IF;
DBMS_OUTPUT.PUT_LINE('Not inserting!');
RETURN unit_id;
exception
when NO_DATA_FOUND then
DBMS_OUTPUT.PUT_LINE('Inserting!');
INSERT INTO depts
(header_id, comments, category)
VALUES
(in_hdr, in_cmt, in_cat)
returning dept_id into unit_id;
COMMIT;
RETURN unit_id;
END get_or_make_unit;

Answer 2

Your call to get_or_make_unit appears to be missing the first parameter.

Answer 3

INSERT INTO depts (
header_id
, comments
, category
) VALUES (
in_hdr
, in_cmt
, in_cat);
This code is not inserting anything into dept_id of depts table. Thats the reason you are getting null