public static function delete_unused() { $query = DB::connection()->prepare("SELECT * FROM Ingredient"); $query->execute(); $rows = $query->fetchAll(); foreach ($rows as $row) { $ingredient = new Ingredient(array('ingredient_id' => $row['id'], 'name' => $row['name'])); if (is_null($ingredient->find_recipes_for_ingredient())) { $ingredient->delete(); } } }