PHP中的继承和函数调用

I can't figure out how to call an insertValue function for the following setup:

This is my bootstrap. It sets my controller and loads its model. (not really important)

<?php
$controller = new Register;
$controller->loadModel('register');
?> 

This is the controller class which has the loadModel function.

class Controller {
public static $model;
public function loadModel($name) {
    $path = 'models/'.$name.'Model.php';
    if(file_exists($path))
    {
        require 'models/'.$name.'Model.php';
        $modelName = $name .'Model';
        $this->model = new $modelName;
    }
}
}

This is the parent model class:

class Model {
public static $database;

function __construct() {
    $this->database = new Database();
}

}

Now the Database class has a function called insertValue() that I want to call, and the register class is where I want to call it from. It's an extension of Controller

The register class appears as follows:

class Register extends Controller {


function __construct() {
    parent::__construct();
    $this->view->render("register", "index", "Register", TRUE);
    }
...
I tried calling it like so:
$this->model->database->insertValue();
but it doesn't even execute.

I think it's because your fields database and model is static. But you are call it dynamicly. Try to remove the static declaration.