From: "Luis C. Ferreira" <lcf@tuxedo.com.ar>
To: Jeff Boes <jboes@nexcerpt.com>, pgsql-sql@postgresql.org
Subject: Re: Rule won't let me NOTIFY, no matter how hard I try
Date: Thu, 15 Jan 2004 15:34:39 -0300
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El Mar 13 Ene 2004 18:07, Jeff Boes escribió:
>JB: Here's the setup: I wanted to write a rule that would fire on an update
>JB: to one table, and do an update to another table, followed by a notify.
>JB: My first attempt wasn't acceptable to PG (7.3.4):
>JB:
>JB: create rule "my_rule" as
>JB: on update to table_A
>JB: where new.col_A != old.col_A
>JB: do
>JB:    (update table_B ...;
>JB:     notify "my_signal";
>JB:    );
>JB:
>JB: ... because you can't have a "notify" statement in a rule that fires on
>JB: update (only select, update, and delete, I guess).
>JB:
hi,

you have to write to rules

first one (update):

create rule "my_rule" as
on update to table_A
 where new.col_A != old.col_A
 do
    update table_B ...;

second one (notify):

create rule "my_rule2" as
on update to table_A
notify my_rule;

	
>JB: Second attempt was to "hide" the notify in a function:
>JB:
>JB: create function fn_notify(TEXT) returns VOID as '
>JB:   execute ''notify " || $1 || "'';
>JB: ' language 'plpgsql';

The correct syntax...

create function fn_notify ( text ) RETURNS void as '
declare
        v_signal alias for $1;
begin
    execute '' notify "'' || v_signal || ''"'';
    return;
end;
  ' language 'plpgsql';

...and re-write the first rule

create rule "my_rule" as
on update to table_A
 where new.col_A != old.col_A
 do
    ( update table_B ...;
	SELECT fn_notify('my_signal'); );

CAVEAT: This rule always returns a tuple:
 fn_notify
-----------

(1 row)


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Luis Carlos Ferreira                          lcf@tuxedo.com.ar 
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