在PHP MVC中访问单例数据库对象时遇到问题

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");
        // (...)
    }