Re: Question on notifications

Alexander Reichstadt wrote:
> Thanks, I had checked the example before but couldn't make sense out
of it in terms of wrapping it in
> Objective-C. I left it in C now and it works fine.
>
> The trigger I am using now looks like this:
>
> CREATE FUNCTION notify_trigger() RETURNS trigger AS $$
>
>
> DECLARE
>
>
> BEGIN
> IF ( TG_OP = 'INSERT' ) THEN
> execute 'NOTIFY ' || TG_TABLE_NAME || '_' || TG_OP || ', ' || NEW.oid;
> ELSE
> execute 'NOTIFY ' || TG_TABLE_NAME || '_' || TG_OP || ', ' || OLD.oid;
> END IF;
> return NULL;
> END;
>
>
> $$ LANGUAGE plpgsql;
>
> it works  if I remove transmission of the OID. If I do transmit the
OID I get
>
>
> DETAIL:  The tuple structure of a not-yet-assigned record is
indeterminate.
> CONTEXT:  PL/pgSQL function "notify_trigger" line 1 at EXECUTE
statement
>
>
> The trigger is firing above function AFTER the TG_OP took place. The
error is thrown upon insertion.
> Doesn't the record exist given I trigger AFTER and not BEFORE the
operation took palce?

Right, and I cannot reproduce the error you get.

Here's what I do (on PostgreSQL 9.1.3):

CREATE OR REPLACE FUNCTION notify_trigger() RETURNS trigger
   LANGUAGE plpgsql AS
$$BEGIN
   EXECUTE 'NOTIFY ' || TG_TABLE_NAME || '_' || TG_OP || ', '''
      || CASE WHEN TG_OP = 'INSERT' THEN NEW.oid ELSE OLD.oid END ||
'''';
   RETURN NEW;
END$$;

Observe that the second argument to NOTIFY is a string.

CREATE TABLE t1(val text, PRIMARY KEY (oid)) WITH OIDS;

CREATE TRIGGER t1_trig AFTER INSERT OR UPDATE OR DELETE ON t1
   FOR EACH ROW EXECUTE PROCEDURE notify_trigger();

INSERT INTO t1 (val) VALUES ('test');
UPDATE t1 SET val=NULL;
DELETE FROM t1;

A second session subscribed to the events gets:

Asynchronous notification "t1_insert" with payload "46728" received from
server process with PID 18687.
Asynchronous notification "t1_update" with payload "46728" received from
server process with PID 18687.
Asynchronous notification "t1_delete" with payload "46728" received from
server process with PID 18687.

Yours,
Laurenz Albe