Compound Trigger to turn a single row into a multirow - oracle

Question

`Basically, i need to create something that when the user insert a value on a table, it turns into a multi insert, he will say the number of rows that will become in a part of table.
But i have 0 ideia from were begin.
My table have COMPMOV - INT: is the number of rows will return.
VLRPROV - NUMBER:
DTVENC - DATE:
PRAZO - INT:
PARCELA - INT:
i started from a another trigger that i created before, but this one i just fill a field that is blank when the user insert.`
CREATE OR replace TRIGGER "TRG_INC_USU_OBSMULTI"
FOR INSERT OR UPDATE
ON AD_OBSMULTI
COMPOUND TRIGGER TYPE R_OBS_TYPE IS RECORD (
OBS_ID AD_OBSMULTI.ID%TYPE,
OBS_IDOBS AD_OBSMULTI.IDOBS%TYPE,
OBS_CODUSU AD_OBSMULTI.CODUSU%TYPE
);
TYPE T_OBS_TYPE IS TABLE OF R_OBS_TYPE INDEX BY PLS_INTEGER;
T_OBS T_OBS_TYPE;
AFTER EACH ROW IS BEGIN
T_OBS (T_OBS.COUNT + 1).OBS_IDOBS := :NEW.IDOBS;
T_OBS (T_OBS.COUNT).OBS_ID := :NEW.ID;
T_OBS (T_OBS.COUNT).OBS_CODUSU := :NEW.CODUSU;
END AFTER EACH ROW;
AFTER STATEMENT IS L_CODUSU AD_OBSMULTI.CODUSU%TYPE;
BEGIN
SELECT
STP_GET_CODUSULOGADO INTO L_CODUSU
FROM
DUAL;
FOR indx IN 1..T_OBS.COUNT
LOOP
IF T_OBS(indx).CODUSU IS NULL THEN
UPDATE
AD_OBSMULTI
SET
CODUSU = L_CODUSU
WHERE
ID = T_OBS(indx).OBS_ID
AND IDOBS = T_OBS(indx).OBS_IDOBS;
END IF;
END LOOP;
END AFTER STATEMENT;
END;
/

Answer 1

A trigger can modify the values of the dml statement (insert/update/delete) only. An additional transaction on the same table within a trigger on that table is generally a bad idea.
But here is a workaround.
Create a table
Create a view on that table
Create an instead of trigger on the view
Insert into the view
Example:
CREATE TABLE MAIN_TABLE (id number);
Table MAIN_TABLE created.
CREATE OR REPLACE VIEW MAIN_VIEW AS
SELECT id, 0 as new_rows FROM MAIN_TABLE;
View MAIN_VIEW created.
INSERT INTO main_view (id) values (100);
1 row inserted.
It is possible to insert into the view. Since there is a 1:1 relationship with the main_table this will insert a row in MAIN_TABLE
SELECT COUNT(*) FROM main_table;
COUNT(*)
----------
1
Now create the instead of trigger on MAIN_VIEW
CREATE OR REPLACE TRIGGER main_view_ioi
INSTEAD OF INSERT
ON main_view
FOR EACH ROW
BEGIN
FOR i IN 1 .. :NEW.NEW_ROWS LOOP
INSERT INTO main_table (id) VALUES (i);
END LOOP;
END;
/
Trigger MAIN_VIEW_IOI compiled
INSERT INTO main_view (id,new_rows) values (1,5);
1 row inserted.
Note that this will say "1 row inserted" because only 1 row was inserted in MAIN_VIEW. However, the instead of trigger created 5 rows in MAIN_TABLE.
SELECT * FROM main_table;
ID
----------
100
1
2
3
4
5