CodeIgniter, Call to a member function post() on a non-object - php

Question

i am new in CodeIgniter (v.2.1.4). I have a problem with getting post from model.
I have a contoller:
class Login extends CI_Controller{
public function index(){
$data['main_view'] = 'login_form';
$this->load->view('login/include/template', $data);
}
public function validate(){
$this->load->library('form_validation');
$this->form_validation->set_rules('user', 'Име', 'trim|required|min_length[3]');
$this->form_validation->set_rules('pass', 'Парола', 'trim|required|min_length[4]');
if($this->form_validation->run()){
$this->load->model('users_model');
if($this->users_model->validate_login($username, $password)){
//valid user
}
else{
//not vlaid user
}
}
else{
$this->index();
}
}
}
and a model:
class Users_model extends CI_Model{
function __construct() {
parent::__construct();
}
function validate_login(){
$username = $this->input->post('user');
$password = md5($this->input->post('pass'));
$this->db->where('username', $username);
$this->db->where('password', $password);
$query = $this->db->get('users');
if($query->num_rows() == 1){
return TRUE;
}
else return FALSE;
}
}
When send via form (post) valid pair (username and password) nothing happens, but in apache2 log appears this:
PHP Fatal error: Call to a member function where() on a non-object in /var/www/ci/application/models/users_model.php
What is wrong?

Answer 1

Add a constructor to the Login class
class Login extends CI_Controller {
public function __construct() {
parent::__construct();
}
}

Answer 2

Do you have database loaded? You need to load the database first.
You can either add it to /config/autoload.php to autoload database function:
$autoload['libraries'] = array('database');
Or call on demand like this:
$this->load->database();
More details here

Answer 3

Do Not Use post in model instead use this in controller like this
controller login.php
public function validate(){
$this->load->library('form_validation');
$this->form_validation->set_rules('user', 'Име', 'trim|required|min_length[3]');
$this->form_validation->set_rules('pass', 'Парола', 'trim|required|min_length[4]');
if($this->form_validation->run()){
$this->load->model('users_model');
$post = $this->input->post();
$data['username'] = $post['username'];
$data['password'] = md5($post['password']);
if($this->users_model->validate_login($data)){
//valid user
}else{
//not vlaid user
}
}
else{
$this->index();
}
}
Model
function validate_login($where){
$this->db->where($where);
$query = $this->db->get('users');
if($query->num_rows() == 1){
return TRUE;
}
return FALSE;
}
This should work. Remember calling post somehow doesn't work in model. I dont exactly know they reason.