thinkphp は add メソッドと save メソッドを呼び出すことができません

public function insert() {	header('Content-type:text/html; charset=utf-8');	date_default_timezone_set('Etc/GMT-8');	$article = M('article');			$data = array();	$data['title'] = $_POST['title'];	$data['author'] = $_SESSION['username'];	$data['category'] = $_POST['category'];	$data['content'] = $_POST['content'];	$data['createtime'] = strtotime(date("Y-m-d"));			if($data['category'] == '请选择' || $data['title']=='') {		$this->error('数据写入不完整，请重新输入');	}	$result = $article->add($data);        }

<?php 	class ArticleModel extends Model {		protected $_validate=array(			array('title','require', '标题不能为空'),			array('author','require', '作者必须要'),			array('category','require', '文章类型不能为空'),			array('content','require','文章内容不能为空'),			array('createtime','require','发表时间必须')		);	} ?>

public function add($data='',$options=array(),$replace=false) {        if(empty($data)) {            // 没有传递数据，获取当前数据对象的值            if(!empty($this->data)) {                $data           =   $this->data;                // 重置数据                $this->data     = array();            }else{                $this->error    = L('_DATA_TYPE_INVALID_');                return false;            }        }        // 分析表达式        $options    =   $this->_parseOptions($options);        // 数据处理        $data       =   $this->_facade($data);        if(false === $this->_before_insert($data,$options)) {            return false;        }        // 写入数据到数据库        $result = $this->db->insert($data,$options,$replace);        if(false !== $result ) {            $insertId   =   $this->getLastInsID();            if($insertId) {                // 自增主键返回插入ID                $data[$this->getPk()]  = $insertId;                $this->_after_insert($data,$options);                return $insertId;            }            $this->_after_insert($data,$options);        }        return $result;    }

    public function insert($data,$options=array(),$replace=false) {        $values  =  $fields    = array();        $this->model  =   $options['model'];        foreach ($data as $key=>$val){            $value   =  $this->parseValue($val);            if(is_scalar($value)) { // 过滤非标量数据                $values[]   =  $value;                $fields[]     =  $this->parseKey($key);            }        }        $sql   =  ($replace?'REPLACE':'INSERT').' INTO '.$this->parseTable($options['table']).' ('.implode(',', $fields).') VALUES ('.implode(',', $values).')';        $sql   .= $this->parseLock(isset($options['lock'])?$options['lock']:false);        return $this->execute($sql);    }