access $this in extended class - php

Question

I've been following a tutorial about OOP programming. And I got this class named User:
class User {
private $_db,
$_data,
$_sessionName,
$_isLoggedIn;
public function __construct($user = null) {
$this->_db = DB::getInstance();
$this->_sessionName = Config::get('session/session_name');
if (!$user) {
if (Session::exists($this->_sessionName)) {
$user = Session::get($this->_sessionName);
if ($this->find($user)) {
$this->_isLoggedIn = true;
} else {
// Process logout
}
}
} else {
$this->find($user);
}
}
public function update($fields = array(), $id = null) {
if (!$id && $this->isLoggedIn()) {
$id = $this->data()->id;
}
if (!$this->_db->update('users', $id, $fields)) {
throw new Exception('De gegevens konden niet gewijzigd worden');
}
}
public function create($fields = array()) {
if (!$this->_db->insert('users', $fields)) {
throw new Exception('Het account is niet aangemaakt');
}
}
public function find($user = null) {
if ($user) {
$field = (is_numeric($user)) ? 'id' : 'email';
$data = $this->_db->get('users', array($field, '=', $user));
if ($data->count()) {
$this->_data = $data->first();
return true;
}
}
}
public function login($email = null, $password = null) {
$user = $this->find($email);
if ($user) {
if ($this->data()->password === hash::make($password)) {
session::put($this->_sessionName, $this->data()->id);
return true;
}
}
return false;
}
public function logout() {
session::delete($this->_sessionName);
}
public function hasPermission($key) {
$group = $this->_db->get('user_role', array('id', '=', $this->data()->rank));
if ($group->count()) {
$permissions = json_decode($group->first()->permission, true);
if ($permissions[$key] == true) {
return true;
}
}
return false;
}
public function data() {
return $this->_data;
}
public function isLoggedIn() {
return $this->_isLoggedIn;
}
}
Each user has different quicklinks stored in the database. I tried to extend the class User with class Link like this:
class Link extends User {
public static function getUserLinks($user) {
if ($user) {
$data = $this->_db->get('user_links', array('uid', '=', $user));
if ($data->count()) {
$this->_data = $data->results();
return $this->_data;
} else {
echo 'No matches found';
}
}
return false;
}
But I get an error message :
Fatal error: Using $this when not in object context in ... on line 153
I thought that when extending a class I can access all the parents details?
What am I doing wrong? Also, is my logic correct behind class Link extends User?
Thanks for the help.

Answer 1

you are trying to access the class pointer within a static method, that's impossible since static methods belongs to the class itself and not to the instance.
you could have a static property that will hold your instance, then you could do that like so: (You'll have to make sure you got an instance of Link)
class Link extends User {
public static $instance;
public function __construct() {
parent::__construct();
self::$instance = $this;
}
public static function getUserLinks($user) {
if (self::$instance instanceof Link && $user) {
$data = self::$instance->_db->get('user_links', array('uid', '=', $user));
if ($data->count()) {
self::$instance->_data = $data->results();
return self::$instance->_data;
} else {
echo 'No matches found';
}
}
return false;
}
}