Php Codeigniter错误选择查询无法检查用户输入

我是codeigniter的新手，我使用的是3.1.5版本。下面是我的用户登录功能

class Auth extends CI_Controller
{
    public function login()
    {
        // Load Login View
        $this->load->view('login');
        // validate form
        $this->form_validation->set_rules('username','Username','required');
        $this->form_validation->set_rules('password','Password','required|min_length[5]');
        if($this->form_validation->run()== true){
            $username = $_POST['username'];
            $password = $_POST['password'];
            // check user in database
            $this->db->select("*");
            $this->db->from("users");
            $this->db->where(array("username"=>$username,"password"=>$password));
            $query = $this->db->get();
            $user_data  = $query->row();
            // check if user exists or not
            if($user_data->username){
                // show temporary success message
                $this->session->set_flashdata("success","User successfully logged in");
                // set temporary sesstion variables
                $_SESSION['user_logged'] = TRUE;
                $_SESSION['username'] = $user_data->username;
            }else{
                $this->session->set_flashdata("error","Invalid username, user not exist");
            }
        }
    }

当我提供用户名和密码等用户凭据时，我遇到以下错误，无法解决此问题

Severity: Notice

Message: Trying to get property of non-object

Filename: controllers/Auth.php

Line Number: 29

Backtrace:

File: D:\xampp\htdocs\ci315\application\controllers\Auth.php
Line: 29
Function: _error_handler

File: D:\xampp\htdocs\ci315\index.php
Line: 315
Function: require_once

29号线就在这里

      if($user_data->username){
       // show temporary success message
       $this->session->set_flashdata("success","User successfully logged in");
         // set temporary sesstion variables
         $_SESSION['user_logged'] = TRUE;
         $_SESSION['username'] = $user_data->username;
         }else{
         $this->session->set_flashdata("error","Invalid username, user not exist");
         }

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如果我对上述部分进行评论，则没有错误。请告诉我哪里做错了。任何帮助都将不胜感激，提前感谢。

下面使用的代码可以很好地工作。如果$query->num\u rows>0而不是 如果$user\u data->username和$query->row->username而不是$user\u data->username

class Auth extends CI_Controller
{
    public function login()
    {
        // Load Login View
        $this->load->view('login');
        // validate form
        $this->form_validation->set_rules('username','Username','required');
        $this->form_validation->set_rules('password','Password','required|min_length[5]');
         if($this->form_validation->run()== true){
            $username = $_POST['username'];
            $password = $_POST['password'];
            // check user in database
            $this->db->select("*");
            $this->db->from("users");
            $this->db->where(array("username"=>$username,"password"=>$password));
            $query = $this->db->get();

            if($query->num_rows() > 0){
                // show temporary success message
                $this->session->set_flashdata("success","User successfully logged in");
                // set temporary sesstion variables
                $_SESSION['user_logged'] = TRUE;
                $_SESSION['username'] = $query->row()->username;
            }else{
                $this->session->set_flashdata("error","Invalid username, user not exist");
            }
        }
    }
}

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感谢您的帮助：