google_forms/application/models/User_model.php

<?php

class User_model extends CI_Model
{
    public function register($enc_password)
    {
        $data = array(
        'email' => $this->input->post('email'),
        'username' => $this->input->post('username'),
        'password' => $enc_password
        );

        return $this->db->insert('users', $data);
    }

    public function login($username, $password)
    {
        $this->db->where('username', $username);
        $this->db->where('password', $password);

        $result = $this->db->get('users');
        if ($result->num_rows() == 1) {
            return $result->row(0)->id;
        } else {
            return false;
        }
    }

    public function check_username_exists($username)
    {
        $query = $this->db->get_where('users', array('username' => $username));
        if (empty($query->row_array())) {
            return true;
        } else {
            return false;
        }
    }

    public function check_email_exists($email)
    {
        $query = $this->db->get_where('users', array('email' => $email));
        if (empty($query->row_array())) {
            return true;
        } else {
            return false;
        }
    }
}