Обсуждение: Rule won't let me NOTIFY, no matter how hard I try

Here's the setup: I wanted to write a rule that would fire on an update 
to one table, and do an update to another table, followed by a notify. 
My first attempt wasn't acceptable to PG (7.3.4):

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

... because you can't have a "notify" statement in a rule that fires on 
update (only select, update, and delete, I guess).

Second attempt was to "hide" the notify in a function:

create function fn_notify(TEXT) returns VOID as ' execute ''notify " || $1 || "'';
' language 'plpgsql';

Oddly enough, this works IF and ONLY IF the rule "my_rule" fires and the 
internal update statement does not update any rows. If it actually 
updates a row, then I get this error:

WARNING:  plpgsql: ERROR during compile of fn_notify near line 5
ERROR:  syntax error at or near ""

What gives? Must I use a trigger to get around this?


-- 
Jeff Boes                                      vox 269.226.9550 ext 24
Database Engineer                                     fax 269.349.9076
Nexcerpt, Inc.                                 http://www.nexcerpt.com           ...Nexcerpt... Extend your Expertise

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_Awhere new.col_A != old.col_Ado   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_Awhere new.col_A != old.col_Ado   ( update table_B ...;SELECT fn_notify('my_signal'); );

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

(1 row)


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