Oracle DBMS INSERT Procedure not working - sql

Question

I'm working on what should be a simple functionality for my database.
When a user signs up to my application, a field password_changed is initialised to 0, upon doing this in my user trigger I want to fire the below method to send that new user a message telling them that they should update their password.
CREATE OR REPLACE TRIGGER trg_users
BEFORE INSERT OR UPDATE ON users FOR EACH ROW
BEGIN
-- Get the new user id
IF :NEW.user_id IS NULL THEN
SELECT seq_user_id.nextval
INTO :NEW.user_id
FROM sys.dual;
END IF;
-- Alert a user that they need to change their password
IF :NEW.pass_changed IS NULL THEN
:NEW.pass_changed := 0;
send_alert(:NEW.user_id, 'Thank-you for registering, please change your password for security reasons!');
END IF;
END;
This first trigger simply initialises password set to 0 and then calls my send_alert() function, taking the :NEW.user_id which gets populated by my sequence.
send_alert() PROCEDURE:
-- Sends an alert to the user noting that they haven't changed their password
CREATE OR REPLACE PROCEDURE send_alert(
this_user users.user_id%TYPE,
this_message STRING
)
AS
BEGIN
INSERT INTO messages
VALUES('', this_user, getSystemId(), 'ALERT', this_message, '', '');
END send_alert;
When this code runs, I get the error integrity constraint (PRCSE.INBOX_MESSAGE_TO_FK) violated - parent key not found I understand what this means - however the value for the parent key should be populated via this_user, if I substitute that field for an existing value the procedure completes and INSERTS for the old user.
I can only think that for some reason the :NEW.user_id is not getting passed, but I initialise its value before calling my procedure.
EDIT 10/04/14 13:48 GMT: To clear any confusion, getSystem() returns the master admin id
-- Gets the ID of the SYSTEM user via its unique email
CREATE OR REPLACE FUNCTION getSystemId
RETURN NUMBER
IS
system_user users.user_id%TYPE;
pragma autonomous_transaction;
BEGIN
SELECT user_id
INTO system_user
FROM users
WHERE user_email = 'system#application.com'
AND user_permissions = 'ADMIN';
RETURN system_user;
COMMIT;
END getSystemId;
Any help would be appreciated -
Regards, Alex.

Answer 1

This is because you try to insert value in BEFORE trigger (e.g. before parent row is inserted):
SQL> create table t(x int primary key);
SQL> create table t_c(x int references t(x));
SQL> create or replace trigger tr_i
2 before insert on t
3 for each row
4 begin
5 insert into t_c(x) values(:new.x);
6 end;
7 /
SQL> insert into t values(1);
insert into t values(1)
*
error in line 1:
ORA-02291: integrity constraint (SCOTT.SYS_C00330529) voilated - parent key not found
ORA-06512: in "SCOTT.TR_I", line 2
ORA-04088: error in trigger execution 'SCOTT.TR_I'
SQL> create or replace trigger tr_i
2 after insert on t
3 for each row
4 begin
5 insert into t_c(x) values(:new.x);
6 end;
7 /
SQL> insert into t values(1);
1 row inserted.
SQL> select * from t;
X
------
1
SQL> select * from t_c;
X
------
1