CREATE EXTENSION lo;
CREATE TABLE image (title text, raster lo);
CREATE TRIGGER t_raster BEFORE UPDATE OR DELETE ON image
    FOR EACH ROW EXECUTE PROCEDURE lo_manage(raster);
SELECT lo_create(43213);
 lo_create 
-----------
     43213
(1 row)

SELECT lo_create(43214);
 lo_create 
-----------
     43214
(1 row)

INSERT INTO image (title, raster) VALUES ('beautiful image', 43213);
SELECT lo_get(43213);
 lo_get 
--------
 \x
(1 row)

SELECT lo_get(43214);
 lo_get 
--------
 \x
(1 row)

UPDATE image SET raster = 43214 WHERE title = 'beautiful image';
SELECT lo_get(43213);
ERROR:  large object 43213 does not exist
SELECT lo_get(43214);
 lo_get 
--------
 \x
(1 row)

-- test updating of unrelated column
UPDATE image SET title = 'beautiful picture' WHERE title = 'beautiful image';
SELECT lo_get(43214);
 lo_get 
--------
 \x
(1 row)

DELETE FROM image;
SELECT lo_get(43214);
ERROR:  large object 43214 does not exist
DROP TABLE image;