我是要用add方法把一个fid字段存到数据库，

添加的时候，把这个直接跟随内容一起入库

public function add() {
       $id = 0;
       $fid = intval(\Phpcmf\Service::L('input')->get('fid'));
       $did = intval(\Phpcmf\Service::L('input')->get('did'));
       $catid = intval(\Phpcmf\Service::L('input')->get('catid'));

       $did && $this->auto_save = 0; // 草稿数据时不加载
       $draft = $did ? $this->content_model->get_draft($did) : [];

       $catid = $draft['catid'] ? $draft['catid'] : $catid;

       // 栏目id不存在时就去第一个可用栏目为catid
       if (!$catid) {
           list($select, $catid) = \Phpcmf\Service::L('Tree')->select_category(
               $this->module['category'],
               $catid,
               'id=\'dr_catid\' name=\'catid\' onChange="show_category_field(this.value)"',
               '', 1, 1, 1
           );
       } else {
           $select = \Phpcmf\Service::L('Tree')->select_category(
               $this->module['category'],
               $catid,
               'id=\'dr_catid\' name=\'catid\' onChange="show_category_field(this.value)"',
               '', 1, 1
           );
       }

       $this->is_get_catid = $catid;
       $draft && $draft['catid'] = $catid;

       list($tpl) = $this->_Post($id, $draft, $fid);

       \Phpcmf\Service::V()->assign([
           'did' => $did,
           'form' =>  dr_form_hidden(['is_draft' => 0, 'module' => MOD_DIR, 'id' => $id]),
           'select' => $select,
           'draft_url' =>\Phpcmf\Service::L('Router')->url(APP_DIR.'/home/add'),
           'draft_list' => $this->content_model->get_draft_list('cid='.$id),
           'menu' => \Phpcmf\Service::M('auth')->_module_menu(
               $this->module,
               ' <i class="'.dr_icon($this->module['icon']).'"></i>  '.dr_lang('%s管理', $this->module['cname']),
               \Phpcmf\Service::L('Router')->url(APP_DIR.'/home/index'),
               \Phpcmf\Service::L('Router')->url(APP_DIR.'/home/add', ['catid' => $catid])
           ),
           'category_field_url' => $this->module['category_data_field'] ?\Phpcmf\Service::L('Router')->url(APP_DIR.'/home/add') : ''
       ]);
       \Phpcmf\Service::V()->display($tpl);
}