fastadmin如何删除、修改where條件裡的值

if ($this->request->isAjax()){
    $filter = json_decode($this->request->get("filter"),true);
    $op     = json_decode($this->request->get("op"),true);
    if(isset($filter['merch_name'])){
        $merch_id = db('merch')->where('name',$filter['merch_name'])->value('id');
        unset($filter['merch_name'],$op['merch_name']);
        if(isset($filter['merch_id'])){
            $filter['merch_id'] = $merch_id.','.$filter['merch_id'];
            $op['merch_id']     = 'in';
        }else{
            $filter['merch_id'] = $merch_id;
            $op['merch_id']     = '=';
        }
        $this->request->get(["filter"=>json_encode($filter),'op'=>json_encode($op)]);
    }
    list($where, $sort, $order, $offset, $limit) = $this->buildparams();
    $total = $this->model->where($where)->order($sort, $order)->count();
    $list  = $this->model->where($where)->order('merch_id', 'desc')->limit($offset, $limit)->select();
    // halt($where);
    $result = array("total" => $total, "rows" => $list);
    return json($result);
}