Re: triggers: dynamic references to fields in NEW and OLD?

Vance Maverick wrote:
> I have a bunch of tables that are similar in some ways, and I'm about to
> put triggers on them.  The triggers will all do essentially the same
> thing -- the only wrinkle is that the name of the column they operate on
> varies from table to table.  I'd like to have just one trigger function,
> written 'dynamically' so it can take the name of the column as a trigger
> parameter (in TG_ARGV).  For example, given tables
>
>   CREATE TABLE a (aa INT);
>   CREATE TABLE b (bb INT);
>
> I'd like to be able to write a trigger function foo() such that with
> trigger declarations
>
>   CREATE TRIGGER a_foo AFTER INSERT OR UPDATE OR DELETE ON a
>     FOR EACH ROW EXECUTE PROCEDURE foo('aa');
>   CREATE TRIGGER b_foo AFTER INSERT OR UPDATE OR DELETE ON b
>     FOR EACH ROW EXECUTE PROCEDURE foo('bb');
>
> the logic in foo() reads columns a.aa or b.bb respectively.
>
> I've tried composing a SQL string including the text 'NEW.aa' or
> 'NEW.bb' appropriately, and then passing this to EXECUTE.  This fails:
>
>   ERROR: NEW used in query that is not in a rule
>
> Any suggestions?
>
If you just need which table triggered the function then |TG_TABLE_NAME|
may be simpler than passing parameters.

Something like this will probably work for you (replace the raise notice
with whatever you have to do)

create or replace function atest() returns trigger as $$
declare
   avalue int;
   tblfld text;
begin
   tblfld := tg_argv[0];
   if tblfld = 'aa' then
      avalue := new.aa;
   else
      if tblfld = 'bb' then
          avalue := new.bb;
      end if;
   end if;
   raise notice '%',avalue;
   return new;
end;
$$ language plpgsql;

klint.

--
Klint Gore
Database Manager
Sheep CRC
A.G.B.U.
University of New England
Armidale NSW 2350

Ph: 02 6773 3789
Fax: 02 6773 3266
EMail: kgore4@une.edu.au