thinkphp5 model 继承报错

[南苑]

在users.php文件中这样写的

namespace  app\index\model;
use think\model;
class  Users extends  Model{

    protected $table ='users';
    protected $field = array('id','u_id','password','is_update','add_time','modify_time','username');
    protected $validate =array(
        array('username','require','用户名不能为空',1),
        array('username','','用户名已存在',1,'unique',1),
        array('password','require','密码不能为空',1),
    );
    protected  $auto=array(
        array('is_update',0),
        array('add_time','time',1,'function'),
    );
}

报class ‘think\model’ not found，请教大神怎么解决啊？在此先谢谢了

[果酱很好吃]

use think\Model; 大小写

[weixin_44423938]

楼上那个大小写也不行，我大小写写对了还是not found