Message: Undefined property: Users::$form_validation - php

Question

im currently trying to change my application from MySQL database to MongoDB database. My project requires to compare two of these, and my MySQL code was working and now it gives me this error.
Stack Trace:
A PHP Error was encountered Severity: Notice Message: Undefined property: Users::$form_validation Filename: controllers/users.php Line Number: 26
Error line:
$this->form_validation->set_rules('username','Username','trim|required|min_length[4]|xss_clean');
Code:
<?php
class Users extends CI_Controller{
public function register(){
$this->form_validation->set_rules('first_name','First Name','trim|required|max_length[50]|min_length[2]|xss_clean');
$this->form_validation->set_rules('last_name','Last Name','trim|required|max_length[50]|min_length[2]|xss_clean');
$this->form_validation->set_rules('email','Email','trim|required|max_length[100]|min_length[5]|xss_clean|valid_email');
$this->form_validation->set_rules('username','Username','trim|required|max_length20]|min_length[6]|xss_clean');
$this->form_validation->set_rules('password','Password','trim|required|max_length[20]|min_length[6]|xss_clean');
$this->form_validation->set_rules('password2','Confirm Password','trim|required|max_length[50]|min_length[2]|xss_clean|matches[password]');
if($this->form_validation->run() == FALSE){
$data['main_content']='users/register';
$this->load->view('layouts/main',$data);
}else{
if($this->User_model->create_member()){
$this->session->set_flashdata('registered','Registered successfully');
redirect('home/index');
}
}
}
public function login(){
//$this->load->model('user_model');
$this->form_validation->set_rules('username','Username','trim|required|min_length[4]|xss_clean');
$this->form_validation->set_rules('password','Password','trim|required|min_length[4]|max_length[50]|xss_clean');
$collection = $this->database->users;
if($this->form_validation->run() == FALSE){
$this->session->set_flashdata('login_failed', 'Sorry, this username doesn't exist.');
redirect('home/index');
} else {
$username=$_POST['login'];
$password=$_POST['password'];
$user_id = $collection->findOne(array('username' => $username, 'password' => md5($password)));
// $username = $this->input->post('username');
// $password = $this->input->post('password');
$user_id = $this->User_model->login_user($username,$password);
if($user_id){
$user_data = array(
'user_id' => $user_id,
'username' => $username,
'logged_in' => true
);
$this->session->set_userdata($user_data);
redirect('home/index');
} else {
$this->session->set_flashdata('login_failed', 'Sorry, this username doesn't exist.');
redirect('home/index');
}
}
}
public function logout(){
$this->session->unset_userdata('logged_in');
$this->session->unset_userdata('user_id');
$this->session->unset_userdata('username');
$this->session->sess_destroy();
redirect('home/index');
}
}

Answer 1

Changing config/autoload.php worked for me, just add form_validation in autoload :
$autoload['libraries'] = array('form_validation');

Answer 2

This because of failed to load relevant library
Method 01
public function __construct()
{
parent::__construct();
$this->load->library('form_validation');
$this->load->helper('form');
}
Method 02
in config/autoload.php
$autoload['libraries'] = array('form_validation');
$autoload['helper'] = array('url', 'form');
Form_Validation Codeigniter

Answer 3

Follow this method-
public function __construct()
{
parent::__construct();
$this->load->library('form_validation');
$this->load->helper('form');
}