Re: Help creating rules/triggers/functions

Blaise Carrupt wrote:
> Hi all !
>
> I use PostgreSQL 7.0.2 on a HP-UX system.
>
> I would like to create a simple function and a simple trigger (or rule) that
> deny a delete from a table if the row is referenced in another table.
>
> I though it should look like this (from my Ingres experience... :) :
>
> create function A_del(int4 i_id)
> BEGIN
> SELECT id
> FROM b
> where a_id = :i_id;
>
> if rowcount > 0 then
> RAISE EXCEPTION "not allowed !"
> end if;
> END
>

CREATE FUNCTION A_del () RETURNS opaque AS '
DECLARE
nrefs integer;
BEGIN
nrefs := count(*) FROM b WHERE a_id = OLD.i_id;
IF nrefs > 0 THEN
RAISE EXCEPTION ''a_id % still referenced from b'', OLD.i_id;
END IF;
RETURN OLD;
END;'
LANGUAGE 'plpgsql';
>
> create trigger before delete from A for each row execute procedure A_del(old.id)

CREATE TRIGGER A_del BEFORE DELETE ON A
FOR EACH ROW EXECUTE PROCEDURE A_del();

>
>
> But it seems to be much more complicated with Postgres (create a C function
> using CurrentTriggerData,...). May I have missed something or is it really much
> more complicated ?

Alternatively (IMHO preferred) you could use a referential
integrity constraint in table B, which would also cover
UPDATE on A and check values inserted/updated into/in B.

CREATE TABLE B ( ...
FOREIGN KEY (i_id) REFERENCES A (a_id)

Jan

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