CREATE TRIGGER enfore_product_nesting_level BEFORE UPDATE ON products
BEGIN
	-- Currently only 1 level is supported
    SELECT CASE WHEN((
        SELECT 1
        FROM products p
        WHERE IFNULL(NEW.parent_product_id, '') != ''
            AND IFNULL(parent_product_id, '') = NEW.id
    ) NOTNULL) THEN RAISE(ABORT, "Unsupported product nesting level detected (currently only 1 level is supported)") END;
END;