notify_changes.sql

CREATE OR REPLACE FUNCTION notify_changes() RETURNS trigger AS $notify_changes$
    DECLARE
        CHANNEL TEXT;
	ID      TEXT;
	JSON    TEXT;
    BEGIN
	CHANNEL := 'changes';
	IF (TG_OP = 'DELETE') THEN
          ID := OLD.id;
        ELSE
	  ID := NEW.id;
        END IF;
	JSON := '{"table_name":"' || TG_TABLE_NAME || '",' ||
	     	 '"operation":"'  || TG_OP || '",' ||
		 '"id":"'         || ID || '"}';
	PERFORM pg_notify(CHANNEL, JSON);
	RETURN NULL;
    END;
$notify_changes$ LANGUAGE plpgsql;

DROP TRIGGER IF EXISTS notify_changes ON table_name;
CREATE TRIGGER notify_changes AFTER DELETE OR INSERT OR UPDATE ON table_name
  FOR EACH ROW EXECUTE PROCEDURE notify_changes();