Re: CASCADE and TRIGGER - Some weird problem - Mailing list pgsql-sql

Hi,
 The issue is due to records in Account_message is still exists for the records which are going to be deleted from the
Messagetable. Please check the sequence of deleting the records. 

When I tried to delete a record using your example, the following exception is raised.

ERROR:  update or delete on "message" violates foreign key constraint "account_message__msg_fkey" on "account_message"
DETAIL:  Key (_message_id)=(2) is still referenced from table "account_message".

Regards,
R.Muralidharan

-----Original Message-----
From: pgsql-sql-owner@postgresql.org
[mailto:pgsql-sql-owner@postgresql.org]On Behalf Of Sonic
Sent: Wednesday, May 04, 2005 1:01 PM
To: pgsql-sql@postgresql.org
Subject: [SQL] CASCADE and TRIGGER - Some weird problem


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Hash: SHA1

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)REFERENCESOWNER(_LOGIN) ON DELETE CASCADE); 

CREATE TABLE ACCOUNT_MESSAGE(_MSG        TEXT,_INDIRIZZO        TEXT,PRIMARY KEY(_MSG,_INDIRIZZO),FOREIGN
KEY(_MSG)REFERENCESMESSAGE(_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)
ONDELETE CASCADE); 

CREATE TABLE MSG_IN_FOLDER(_MSG        TEXT,_FOLDER        TEXT,PRIMARY KEY(_MSG,_FOLDER),FOREIGN KEY(_MSG)REFERENCES
MESSAGE(_MESSAGE_ID),FOREIGNKEY(_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_MESSAGENATURAL 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_FOLDERFOR 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 ('anna@gmail.com', 'anna');
insert into ACCOUNT values ('paolo@gmail.com', 'paolo');
insert into MESSAGE (_message_id) values ('1');
insert into MESSAGE (_message_id) values ('2');
insert into ACCOUNT_MESSAGE values ('1', 'anna@gmail.com');
insert into ACCOUNT_MESSAGE values ('1', 'paolo@gmail.com');
insert into ACCOUNT_MESSAGE values ('2', 'anna@gmail.com');
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_MESSAGENATURAL 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_FOLDERFOR 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

sonicaaaa@gmail.com
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