Having Issue on Accessing Singleton Database Object In PHP MVC - php

Question

I am having trouble on accessing to an instance of a singleton class in PHP MVC. Basically the MVC looks like
First of all I have included and instantiated objects in the init.php as
// include objects
include('app/Database.php');
include('app/models/m_template.php');
include('app/models/m_categories.php');
// create objects
$tdatabase = new Database();
$Template = new Template();
$Categories = new Categories();
and in m_categories.php I tried to use the $tdatabase object as:
<?php
class Categories {
private $db_table = 'category';
function __construct() { }
public function get_categories() {
$data = array();
$res = $tdatabase->query("SELECT * FROM " . $this->db_table . " ORDER BY name");
foreach ($res as $dataRow):
$data[] = array('id' => $dataRow['id'],
'name' => $dataRow['name'],
'img' => $dataRow['img'],
'alt' => $dataRow['alt'],
);
endforeach;
return $data;
}
}
and finally in index.php I have:
<?php
include('app/init.php');
echo '<pre>';
print_r($Categories->get_categories());
echo '</pre>';
but I am getting following errors:
can you please let me know why this is happening and how I can fix this?
Update 1:
Update 2

Answer 1

Categories object doesn't have any information about outside variables. You sholud pass Database object to your Categories object e.g. by constructor or by method parameter.
init.php
$tdatabase = new Database();
$Template = new Template();
$Categories = new Categories($tdatabase);
m_categories.php
class Categories {
protected $database;
private $db_table = 'category';
function __construct($database) {
$this->database = $database;
}
public function get_categories() {
$data = array();
$res = $this->database->query("SELECT * FROM " . $this->db_table . " ORDER BY name");
// (...)
}

Answer 2

your variable tdatabase is out of scope. you either need to pass it into the function, or set it as a class member variable in the constructor or via a setter
i.e.
public function get_categories(Database $tdatabase) {
$data = array();
$res = $tdatabase->query("SELECT * FROM " . $this->db_table . " ORDER BY name");
I often see code like this though, and I (almost) always recommend, especially for new projects that you use the model/mapper pattern because it is more easily extensible and is more maintainable. See here for an example:
OOP PHP PDO My First Project , Am I doing right?