Subject: Re: How to avoid (stop) a endless loop in a trigger
From: Oliver Elphick <olly@lfix.co.uk>
Reply-To: olly@lfix.co.uk
To: Rodrigo Sakai <rodrigo@2bfree.com.br>
Cc: pgsql-sql@postgresql.org
In-Reply-To: <20040304145407.32236.qmail@hm10.locaweb.com.br>
References: <20040304145407.32236.qmail@hm10.locaweb.com.br>
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Date: Thu, 04 Mar 2004 15:13:53 +0000
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On Thu, 2004-03-04 at 14:54, Rodrigo Sakai wrote:
>   Hi people, i have a problem here.
>   I'm doing a trigger that when a update occurs i need to do an update on the same table (target table), but as known, it causes a endless loop whithin infinit updates.   So I need to stop the trigger after it does the first update, is there any way?????
>   I tried to do a return null, but that was a very bad idea because it stops completly the function fired by a trigger and all its computation is in vain...
> 
>   The test trigger that i did is like :
> 
> CREATE OR REPLACE FUNCTION public.sp_teste_loop()  RETURNS trigger AS '
>   begin
>     raise notice \'Trigger Fired\';
>     if (TG_OP = \'INSERT\') then
>       update teste_trigger
>         set flg_bool = \'S\'
>         where codigo=NEW.codigo;
> 
>       RETURN NEW;
>       
>     elsif (TG_OP = \'UPDATE\') then
>       update teste_trigger
>         set flg_bool = \'N\'
>       where codigo=NEW.codigo;
> 
>       RETURN NULL;
>     end if;
>   end;
> '  LANGUAGE 'plpgsql' VOLATILE;

Does this update other records, or only the one you are inserting or
updating?

If the former, add " AND flg_bool IS NULL OR flg_bool != \'S\'" to the
update condition (!=\'N\' for the update case); then records that are
already OK will not be touched, so the recursion will stop
automatically.

If the latter, just change NEW.flg_bool and return NEW

> CREATE TRIGGER tr_sp_teste_trigger
>   BEFORE INSERT OR UPDATE
>   ON public.teste_trigger
>   FOR EACH ROW
>   EXECUTE PROCEDURE public.sp_teste_loop();
> 
>   Thank for any help and regards!!!!
> 
> 
> =====================
> Rodrigo Sakai
> Database Programmer
> rodrigo@2bfree.com.br
> http://www.2bfree.com.br
> Tel:  (55) (11) 5083-5577
> Fax: (55) (11) 5549-3598
> =====================
> 
> 
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