<?php
namespace Joy\Classes\MVCClasses;
class Model {
  private $_connection;

  public function setConnection($connection) {
    $this->_connection = $connection;
  }

  public function getConnection() {
    return $this->_connection;
  }
}
//Setze so Connection:
$model = new \Joy\Classes\MVCClasses\Model;
$model->setConnection($mysqlClass->DBConnect());
//Rufe $getConnection() auf
$this->getConnection()->query('SELECT * FROM test'); //= NULL, wieso auch immer...