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hi, have a little problem with a trigger and the ON DELETE CASCADE
statement.
i'm working on a db that represents Users and Messages. A message can be
owned by more than a user. if i delete a user all his related objects
are deleted too (ON DELETE CASCADE), but if a message that this user
owns is also owned by another user, it has not to be deleted.
i just put ON DELETE CASCADE statement on foreign keys and thos seem to
work.
then i wrote a trigger to check if each message the user owns is owned
by someone else. if it's not delete it!
- -----------------------------------------------------------
- -----this is the code:
CREATE TABLE OWNER(
_LOGIN TEXT,
PRIMARY KEY(_LOGIN) );
CREATE TABLE MESSAGE(
_MESSAGE_ID TEXT,
PRIMARY KEY(_MESSAGE_ID)
);
CREATE TABLE ACCOUNT(
_INDIRIZZO TEXT UNIQUE,
_LOGIN TEXT,
PRIMARY KEY(_INDIRIZZO,_LOGIN),
FOREIGN KEY(_LOGIN)REFERENCES OWNER(_LOGIN) ON DELETE CASCADE);
CREATE TABLE ACCOUNT_MESSAGE(
_MSG TEXT,
_INDIRIZZO TEXT,
PRIMARY KEY(_MSG,_INDIRIZZO),
FOREIGN KEY(_MSG)REFERENCES MESSAGE(_MESSAGE_ID),
FOREIGN KEY(_INDIRIZZO)REFERENCES ACCOUNT(_INDIRIZZO) ON DELETE
CASCADE);
CREATE TABLE FOLDER(
_PATH TEXT,
_OWNER TEXT,
PRIMARY KEY(_PATH),
FOREIGN KEY(_OWNER)REFERENCES OWNER(_LOGIN) ON DELETE CASCADE);
CREATE TABLE MSG_IN_FOLDER(
_MSG TEXT,
_FOLDER TEXT,
PRIMARY KEY(_MSG,_FOLDER),
FOREIGN KEY(_MSG)REFERENCES MESSAGE(_MESSAGE_ID),
FOREIGN KEY(_FOLDER)REFERENCES FOLDER(_PATH) ON DELETE CASCADE);
CREATE FUNCTION check_message() RETURNS trigger AS $check_MESSAGE$
BEGIN
DELETE FROM MESSAGE WHERE _message_id IN ( SELECT _MSG
FROM ACCOUNT_MESSAGE NATURAL
JOIN msg_in_FOLDER
WHERE _MSG = OLD._MSG
GROUP BY _MSG
HAVING count(*)=1
);
RAISE NOTICE 'Value of OLD._MSG %', OLD._MSG;
RETURN NULL;
END;
$check_MESSAGE$ LANGUAGE plpgsql;
CREATE TRIGGER check_message AFTER DELETE ON MSG_IN_FOLDER
FOR EACH ROW EXECUTE PROCEDURE check_message();
- -------------------------------------------------
- --and these are some values:
delete from OWNER;
delete from ACCOUNT;
delete from MESSAGE;
delete from ACCOUNT_MESSAGE;
delete from FOLDER;
delete from MSG_IN_FOLDER;
insert into OWNER (_login) values ('anna');
insert into OWNER (_login) values ('paolo');
insert into ACCOUNT values ('[EMAIL PROTECTED]', 'anna');
insert into ACCOUNT values ('[EMAIL PROTECTED]', 'paolo');
insert into MESSAGE (_message_id) values ('1');
insert into MESSAGE (_message_id) values ('2');
insert into ACCOUNT_MESSAGE values ('1', '[EMAIL PROTECTED]');
insert into ACCOUNT_MESSAGE values ('1', '[EMAIL PROTECTED]');
insert into ACCOUNT_MESSAGE values ('2', '[EMAIL PROTECTED]');
insert into FOLDER (_path, _OWNER) values ('c', 'anna');
insert into MSG_IN_FOLDER values ('1', 'c');
insert into MSG_IN_FOLDER values ('2', 'c');
select * from MESSAGE;
- ----------
as you see there are 2 messages. message 1 is owned both by 'anna' and
'paolo'. message 2 is owned just by 'anna'.
now what i want is that if i delete user 'anna' just message 2 is deleted.
i guess i've done that with my trigger:
...
CREATE FUNCTION check_message() RETURNS trigger AS $check_MESSAGE$
BEGIN
DELETE FROM MESSAGE WHERE _message_id IN ( SELECT _MSG
FROM ACCOUNT_MESSAGE NATURAL
JOIN msg_in_FOLDER
WHERE _MSG = OLD._MSG
GROUP BY _MSG
HAVING count(*)=1
);
RAISE NOTICE 'Value of OLD._MSG %', OLD._MSG;
RETURN NULL;
END;
$check_MESSAGE$ LANGUAGE plpgsql;
CREATE TRIGGER check_message AFTER DELETE ON MSG_IN_FOLDER
FOR EACH ROW EXECUTE PROCEDURE check_message();
...
i'm also sure that values it process are right beacuse of that RAISE
NOTICE 'Value of OLD._MSG %', OLD._MSG;
but something seems to go wrong.
all 'anna' stuff is deleted but not her message 2 !
DELETE FROM owner WHERE _login = 'anna';
SELECT * FROM message;
can someone help me to understand why this is not done?
i don't receive any error message from postgres...
thanks
paolo from italy
[EMAIL PROTECTED]
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TIP 9: the planner will ignore your desire to choose an index scan if your
joining column's datatypes do not match
