CREATE OR REPLACE FUNCTION tree_insert() RETURNS trigger AS '
DECLARE
	i RECORD;
	child integer[2];
BEGIN
	FOR i IN EXECUTE ''SELECT node, kids FROM ''||TG_RELNAME||''_tree WHERE id = ''||NEW.parent LOOP
		child := tree_child(i.node, i.kids+1);

		EXECUTE ''INSERT INTO ''||TG_RELNAME||''_tree (id, node, kids) ''
			||''VALUES(''||NEW.id||'', ARRAY[''||child[1]||'',''||child[2]||''], 0)'';

		EXECUTE ''UPDATE ''||TG_RELNAME||''_tree SET kids = kids + 1 WHERE id = ''||NEW.parent;

	END LOOP;
	IF NOT FOUND THEN
		RAISE EXCEPTION ''Parent % does not exist'', NEW.parent;
	END IF;
	RETURN NEW;
END;
' LANGUAGE plpgsql;

CREATE OR REPLACE FUNCTION tree_delete() RETURNS trigger AS '
DECLARE
BEGIN
	IF 1 = OLD.id THEN
		RAISE EXCEPTION ''You can not delete the root node of a tree'';
	END IF;
	EXECUTE ''UPDATE ''||TG_RELNAME||''_tree SET kids = kids - 1 WHERE id = ''||OLD.parent;
	RETURN OLD;
END;
' LANGUAGE plpgsql;