How to query if there is data in thinkphp

       //字符过滤
       $mode = M("gkwh_dictdata"); // 实例化对象
       $where = "data_value = '".trim($_POST["famiMembFana"])."' or data_value = '".trim($_POST["famiMembLana"])."'";
       $list_dictdata = $mode->where($where)->find(); 
 
       //如果记录存在    
       if($list_dictdata !== null) {
          $obj->code = -1;
         
          $msg = "注册信息有非法字符";
       $obj->msg = $msg;
       $obj->data  = $list_dictdata;      
       $obj->count = 0;
       echo json_encode($obj);
       die;
       }