http://localhost/bbs/board/lists/ci_board/ 이대로가면 목록보기가 안되네요

A PHP Error was encountered

Severity: Notice

Message: Undefined property: Board::$db

Filename: core/Model.php

Line Number: 52

Fatal error: Call to a member function query() on a non-object in E:\xampp\htdocs\bbs\application\models\board_m.php on line 46

가보면 sql 

$sql = "SELECT * FROM ".$table.$sword." ORDER BY board_id DESC" .$limit_query;           

$query = $this->db->query($sql);

이부분 문제인데 110p까지 그냥 소스 코딩하면서 잘 되던게 

예제 소스받아서 그냥 덮어버리니까 갑자기 이러네요 -_-?

ㅠㅠ