在第二个触发器上插入值，并从第一个触发器PL \\ SQL中插入值

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;
/