public function find($id=''){

        if(!isset($id) || !is_numeric($id)){

            echo '数据传入有误，请重试';

        }

        $select_obj2 = [];

        $select_obj = DB::table('student')

                      ->whereRaw('id>=? and password !=?',[$id,''])

                      ->select('id',DB::raw(" count('username') as usernamecount "))

                      ->first();

        foreach ($select_obj as $k=>$v){

            $select_obj2[$k] = $v;

        }

        /* DB查询构造器数据转换成模型数据collect instance */

        $collectInstance = collect($select_obj);

        var_dump($collectInstance); //查询构造器对象

        var_dump($collectInstance->toArray());  //collect模型instance实例

        var_dump($select_obj);  //object对象

        var_dump($select_obj2); //Array数组

    }