How to dynamically display user name from the database after log in? - php

Question

I need to dynamically display user name from logged in user in my OOP PHP project. I can display it when I type right id from the database but it shows error when I try to define property $user_id in my function find_by_id. I need help on how to define $user_id variable. Here is my code:
index.php
<?php $user = User::find_by_id($user_id); ?>
<h1>Hello, <?php echo $user->username; ?></h1>
user.php
<?php
class User
{
protected static $db_table = "users";
public $id;
public $username;
public $password;
public $first_name;
public $last_name;
private function has_the_attribute($the_attribute)
{
$object_properties = get_object_vars($this);
return array_key_exists($the_attribute, $object_properties);
}
public static function instantation($the_record)
{
$the_object = new self;
foreach ($the_record as $the_attribute => $value) {
if ($the_object->has_the_attribute($the_attribute)) {
$the_object->$the_attribute = $value;
}
}
return $the_object;
}
public static function find_this_query($sql)
{
global $database;
$result_set = $database->query($sql);
$the_object_array = [];
while ($row = mysqli_fetch_array($result_set)) {
$the_object_array[] = self::instantation($row);
}
return $the_object_array;
}
public static function find_all()
{
return self::find_this_query("SELECT * FROM " . static::$db_table . " ");
}
public static function find_by_id($user_id)
{
global $database;
$the_result_array = self::find_this_query("SELECT * FROM " . self::$db_table . " WHERE id = $user_id");
return !empty($the_result_array) ? array_shift($the_result_array) : false;
}
public static function verify_user($username, $password)
{
global $database;
$username = $database->escape_string($username);
$password = $database->escape_string($password);
$sql = "SELECT * FROM " . self::$db_table . " WHERE ";
$sql .= "username = '{$username}' ";
$sql .= "AND password = '{$password}'";
$the_result_array = self::find_this_query($sql);
return !empty($the_result_array) ? array_shift($the_result_array) : false;
}
}
$user = new User();
session.php
<?php
class Session
{
private $signed_in = false;
public $user_id;
public $message;
public function __construct()
{
session_start();
$this->check_the_login();
$this->check_message();
}
public function login($user)
{
if ($user) {
$this->user_id = $_SESSION['user_id'] = $user->id;
$this->signed_in = true;
}
}
public function logout()
{
unset($_SESSION['user_id']);
unset($this->user_id);
$this->signed_in = false;
}
private function check_the_login()
{
if (isset($_SESSION['user_id'])) {
$this->user_id = $_SESSION['user_id'];
$this->signed_in = true;
} else {
unset($this->user_id);
$this->signed_in = false;
}
}
public function is_signed_in()
{
return $this->signed_in;
}
public function message($msg="")
{
if (!empty($msg)) {
$_SESSION['message'] = $msg;
} else {
return $this->message;
}
}
public function check_message()
{
if (isset($_SESSION['message'])) {
$this->message = $_SESSION['message'];
unset($_SESSION['message']);
} else {
$this->message = "";
}
}
}
$session = new Session();

Answer 1

For the sake of marking this as accepted, what you need to do is actually pass the user ID of the and not just an uninitialised variable, if your instance you are storing it in the session so I presume it would be:
<?php $user = User::find_by_id($_SESSION['user_id']); ?>
Note: To make your templating cleaner, you can use the shorthand syntax for echo:
<h1>Hello, <?= $user->username; ?></h1>
Another thing to note is that you have built a Session class, however you are still for some reason accessing the data through $_SESSION which doesn't make sense, make some setters / getters for it. Finally, sessions are something that you'll be using a lot therefore it would be worth making that class static.
Reading Material
echo