thinkphp增加字段搜索内容

怎么增加其他字段搜索
这个是thinkphp后台
目前只有搜索标题title想增加其他字段上去

SearchAction.class.php

<form action="/?m=search" method="post">
            <input type="hidden" name="modelid" value="9" id="modelid2">
            <input type="text" class="chunk" name="keyword" placeholder="请输入您要查询的条件" />
            <button type="submit" class="" value="" target="menuFrame" />点击查询</button>
</form>

<?php

class SearchAction extends PublicAction
{

    public function index()
    {
        $keyword = $_GET['keyword'] = I('keyword');
        $modelid = $_GET['modelid'] = I('modelid', 9, 'intval');

        $this->assign(I('request.'));
        
        //可搜索内容模型
        $model_search = array();
        foreach ($this->Model as $val) {
            if ($val['issearch'] == 1) {
                $model_search[] = $val;
            }
        }
        $this->assign('model_search', $model_search);

        $this->assign('seo_title', $this->Config['seo_title']);
        $this->assign('seo_keywords', $this->Config['seo_keywords']);
        $this->assign('seo_description', $this->Config['seo_description']);

        $modelname = $this->Model[$modelid]['tablename'];

        $where = array();
        $where['status'] = 1;
        $where['lang'] = LANG_ID;

        $where['title'] = array('like',"%$keyword%");

        $db = M($modelname);
        $count = $db->where($where)->count();
        
        if($count) {
            import("@.ORG.Page");
            $page = new Page($count, 1);
            $pages = $page->show();
            
            $field = 'id,url,title,keywords,description,thumb,createtime,tel';

            $list = $db->field($field)->where($where)->order('listorder desc,id desc')->limit($page->firstRow . ',' . $page->listRows)->select();

            $this->assign('pages', $pages);
            $this->assign('list', $list);
        }
        
        fangke_log('search','index',0,$keyword);
        
        $this->assign(I('get.'));
        $this->display();
    }
}