$Form->where('id=' . $id)->setField($key,$value); /home/Form/update_field?id=1&key=title&value=ThinkPHP1

    //http://localhost/thinkphp323/index.php/home/Form/update_field?id=1&key=title&value=ThinkPHP1
    public function update_field($id=1,$key='title',$value='ThinkPHP'){
        $Form = M("Form");
        // 更改title值
        $Form->where('id=' . $id)->setField($key,$value);
    }