Postgresql trigger operating on both NEW and OLD records - postgresql

Question

This is primarily a style question.
I have an AFTER INSERT OR UPDATE trigger. I want to run the same query against whichever of the the NEW/OLD records are available. Rather than have conditionals checking TG_OP and duplicating the query, what is the cleanest way to determine which are available and to loop over them?
Example code:
CREATE FUNCTION myfunc() RETURNS TRIGGER AS $$
DECLARE
id int;
ids int[];
BEGIN
IF TG_OP IN ('INSERT', 'UPDATE') THEN
ids := ids || NEW.id;
END IF;
IF TG_OP IN ('UPDATE', 'DELETE') THEN
ids := ids || OLD.id;
END IF;
FOREACH id IN ARRAY ARRAY(SELECT DISTINCT UNNEST(ids))
LOOP
RAISE NOTICE 'myfunc called for % on id %', TG_OP, id;
/* RUN QUERY REFERENCING id */
END LOOP;
RETURN NULL;
END;
$$ LANGUAGE plpgsql;
Is there a shorter/simpler/more idiomatic way to achieve that?

Answer 1

Array handling and a separate SELECT DISTINCT seem too expensive for the job. This should be cheaper:
CREATE FUNCTION myfunc()
RETURNS TRIGGER AS
$func$
DECLARE
_id int;
BEGIN
CASE TG_OP
WHEN 'INSERT', 'UPDATE' THEN
_id := NEW.id;
WHEN 'DELETE' THEN
_id := OLD.id;
END CASE;
FOR i IN 1..2 -- max 2 iterations
LOOP
RAISE NOTICE 'myfunc called for % on id %', TG_OP, _id;
/* RUN QUERY REFERENCING _id */
EXIT WHEN TG_OP <> 'UPDATE' OR i = 2; -- only continue in 1st round for UPDATE
EXIT WHEN _id = OLD.id; -- only continue for different value
_id := OLD.id;
END LOOP;
RETURN NULL;
END
$func$ LANGUAGE plpgsql;
Related:
BREAK statement in PL/pgSQL
But I would probably just write a separate trigger function & trigger for each DML statement. Rather three very simple and faster functions than one generic but complex and slower one.