Insert value on second trigger with value from first trigger PL\SQL - sql

Question

Hi I try to Insert value in the second trigger with new id from first trigger only if condition is fulfiled, but I'm stuck.
table1_trg works
CREATE TABLE table1 (
id NUMBER(9,0) NOT NULL,
subject VARCHAR2(200) NOT NULL,
url_address VARCHAR2(200) NOT NULL,
)
CREATE OR REPLACE TRIGGER table1_trg
BEFORE INSERT ON table1
FOR EACH ROW
BEGIN
SELECT table1_seq.NEXTVAL
INTO :new.id
FROM dual;
END;
/
CREATE OR REPLACE TRIGGER table1_url
BEFORE INSERT ON table1
FOR EACH ROW
WHEN (NEW.subject = 'Task')
BEGIN
INSERT INTO CSB.table1 (url_address)
VALUES ('blabla.com?' || :new.id);
END;
/
I insert only subject but after that i receive exception that subject can not be null.
INSERT INTO corp_tasks_spec (subject) VALUES ('Task')
Any ideas how to resolve it?

Answer 1

You should not be inserting a new record into the same table, you should be modifying the column values for the row you're already inserting - which the trigger is firing against. You're getting the error because of that second insert - which is only specifying the URL value, not the subject or ID (though the first trigger would fire again and set the ID for that new row as well - so it complains about the subject).
Having two triggers on the same firing point can be difficult in old versions of Oracle as the order they fired wasn't guaranteed - so for instance your second trigger might fire before the first, and ID hasn't been set yet. You can control the order in later versions (from 11g) with FOLLOWS:
CREATE OR REPLACE TRIGGER table1_url
BEFORE INSERT ON table1
FOR EACH ROW
FOLLOWS table1_trg
WHEN (NEW.subject = 'Task')
BEGIN
:NEW.url_address := 'blabla.com?' || :new.id;
END;
/
This now fires after the first trigger, so ID is set, and assigns a value to the URL in this row rather than trying to create another row:
INSERT INTO table1 (subject) VALUES ('Task');
1 row inserted.
SELECT * FROM table1;
ID SUBJECT URL_ADDRESS
---------- ---------- --------------------
2 Task blabla.com?2
But you don't really need two triggers here, you could do:
DROP TRIGGER table1_url;
CREATE OR REPLACE TRIGGER table1_trg
BEFORE INSERT ON table1
FOR EACH ROW
BEGIN
:NEW.id := table1_seq.NEXTVAL; -- no need to select from dual in recent versions
IF :NEW.subject = 'Task' THEN
:NEW.url_address := 'blabla.com?' || :new.id;
END IF;
END;
/
Then that trigger generates the ID and sets the URL:
INSERT INTO table1 (subject) VALUES ('Task');
1 row inserted.
SELECT * FROM table1;
ID SUBJECT URL_ADDRESS
---------- ---------- --------------------
2 Task blabla.com?2
3 Task blabla.com?3
Of course, for anything except Task you'll have to specify the URL as part of the insert, or it will error as that is a not-null column.

Answer 2

Create sequence
CREATE SEQUENCE table1_SEQ
START WITH 1
MAXVALUE 100000
MINVALUE 1
NOCYCLE
NOCACHE
NOORDER;
CREATE TRIGGER
CREATE OR REPLACE TRIGGER table1_TRG
Before Insert
ON table1 Referencing New As New Old As Old
For Each Row
Declare V_Val Number;
Begin
Select table1_SEQ.NextVal into V_Val From Dual;
If Inserting Then
:New.id:= V_Val;
End If;
End;
/