Philipp Kraus wrote:
Yes; here is an example:

test=> CREATE TABLE lo_test (id integer PRIMARY KEY, lob oid);

test=> CREATE OR REPLACE FUNCTION lo_trigger() RETURNS trigger
LANGUAGE plpgsql AS
$$BEGIN
IF TG_OP = 'UPDATE' OR TG_OP = 'DELETE' THEN
IF OLD.lob IS NOT NULL THEN
IF TG_OP = 'DELETE' THEN
PERFORM lo_unlink(OLD.lob);
ELSEIF (NEW.lob IS NULL OR OLD.lob != NEW.lob) THEN
PERFORM lo_unlink(OLD.lob);
END IF;
END IF;
END IF;
IF TG_OP = 'UPDATE' OR TG_OP = 'INSERT' THEN
RETURN NEW;
ELSE
RETURN OLD;
END IF;
END;$$;

test=> CREATE TRIGGER lo_trigger AFTER UPDATE OR DELETE ON lo_test
FOR EACH ROW EXECUTE PROCEDURE lo_trigger();

test=> \lo_import schiach.jpg
lo_import 20337

test=> INSERT INTO lo_test (id, lob) VALUES (1, 20337);
INSERT 0 1

test=> \lo_list
Large objects
ID | Description
-------+-------------
20337 |
(1 row)

test=> DELETE FROM lo_test WHERE id=1;
DELETE 1

test=> \lo_list
Large objects
ID | Description
----+-------------
(0 rows)

Yours,
Laurenz Albe