Abstract
Model View Controller.This tutorial will take you from the beginning to the end of building a MVC framework. The object is not soley to produce the finished MVC framework, although that will happen, but to demonstrate how MVC works and some of the concepts that lay behind it..
What is MVC?
MVC is a design pattern. A Design pattern is a code structure that allows for common coding frameworks to be replicated quickly. You might think of a design pattern as a skeleton or framework on which your application will be built.In the MVC framework that is created in this tutorial, several key points will be raised. The first is the frameworks needs a single point of entry, ie: index.php. This is where all access to the site must be controlled from. To ensure that a single point of entry is maintained, htaccess can be utilized to ensure no other file may be accessed, and that we hide the index.php file in the url. Thus creating SEO and user friendly URL's.
It is beyond the scope of this tutorial to show how to set up htaccess and mod_rewrite and more information on these can be gained from the Apache manual. The .htaccess file itself looks like this.
RewriteEngine on
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^(.*)$ index.php?rt=$1 [L,QSA]
The .htaccess file will permit access to the site via urls such asRewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^(.*)$ index.php?rt=$1 [L,QSA]
http://www.example.com/news/show
If you do not have mod_rewrite available, the entry to the site will be the same, except that the URL will contain the values needed such as:
http://www.example.com/index.php?rt=news/show
The Site Structure
In this tutorial several directories are required to hold the various components that make up the MVC framework. The index.php and the .htaccess files will, of course, reside at the top level. We will need a directory to hold the application code, and directories for the model view and controllers. The site structure should look like this: html
application
controller
includes
model
views
.htaccess
index.php
application
controller
includes
model
views
.htaccess
index.php
The Index File
As previously mentioned, the index.php file is our single point of access. As such, it provides the ideal space for declaring variables and site wide configurations. It is in this file that we will also call a helper file to initialize a few values. This file will be called init.php and it will be placed in includes directory as shown in the direcory structure. The index file therefore, will begin like this:
<?php
/*** error reporting on ***/
error_reporting(E_ALL);
/*** define the site path constant ***/
$site_path = realpath(dirname(__FILE__));
define ('__SITE_PATH', $site_path);
/*** include the init.php file ***/
include 'includes/init.php';
?> Of course, to create new object we need to include the registry class definition file. During the building of the MVC framework we will be including the application class files directly. Any PHP class definition files which are used by the model will be autoloaded as they can become quite cumbersome with larger applications. To alleviate some of this PHP has the __autoload function to help us out. After the application includes, the __autoload function will immediately follow to load class definition files automatically when they are required by the system. That is, when the new keyword is used. The class definitions will be stored in a directory called model. The includes/init.php file should now look like this.
<?php
/*** include the controller class ***/
include __SITE_PATH . '/application/' . 'controller_base.class.php';
/*** include the registry class ***/
include __SITE_PATH . '/application/' . 'registry.class.php';
/*** include the router class ***/
include __SITE_PATH . '/application/' . 'router.class.php';
/*** include the template class ***/
include __SITE_PATH . '/application/' . 'template.class.php';
/*** auto load model classes ***/
function __autoload($class_name) {
$filename = strtolower($class_name) . '.class.php';
$file = __SITE_PATH . '/model/' . $filename;
if (file_exists($file) == false)
{
return false;
}
include ($file);
}
/*** a new registry object ***/
$registry = new registry;
?> <?php
?> - controller_base.class.php
- registry.class.php
- router.class.php
- template.class.php
The Registry
The registry is an object where site wide variables can be stored without the use of globals. By passing the registry object to the controllers that need them, we avoid pollution of the global namespace and render our variables safe. We need to be able to set registry variables and to get them. The php magic functions __set() and __get() are ideal for this purpose. So, open up the registry.class.php in the applications directory and put the following code in it:
<?php
Class Registry {
/*
* @the vars array
* @access private
*/
private $vars = array();
/**
*
* @set undefined vars
*
* @param string $index
*
* @param mixed $value
*
* @return void
*
*/
public function __set($index, $value)
{
$this->vars[$index] = $value;
}
/**
*
* @get variables
*
* @param mixed $index
*
* @return mixed
*
*/
public function __get($index)
{
return $this->vars[$index];
}
}
?> The Model
The Model is the "M" in MVC. The model is where business logic is stored. Business logic is loosely defined as database connections or connections to data sources, and provides the data to the controller. As I am a fan of CAV (Controller Action View) we will blur the line between the Model and Controller. This is not strictly how MVC should work, but this is PHP baby. Our database connection is a simple singleton design pattern and resides in the classes directory and can be called statically from the controller and set in the registry. Add this code to the init.php file we created earlier.
<?php
/*** create the database registry object ***/
$registry->db = db::getInstance();
?> The Router
The router class is responsible for loading up the correct controller. It does nothing else. The value of the controller comes from the URL. The url will look a like this:http://www.example.com/index.php?rt=news
or if you have htaccess amd mod_rewrite working like this:
http://www.example.com/news
As you can see, the route is the rt variable with the value of news. To begin the router class a few things need to be set. Now add this code to the router.class.php file in the application directory.
<?php
class router {
/*
* @the registry
*/
private $registry;
/*
* @the controller path
*/
private $path;
private $args = array();
public $file;
public $controller;
public $action;
function __construct($registry) {
$this->registry = $registry;
}
/*** load the router ***/
$registry->router = new router($registry);
<?php
/**
*
* @set controller directory path
*
* @param string $path
*
* @return void
*
*/
function setPath($path) {
/*** check if path i sa directory ***/
if (is_dir($path) == false)
{
throw new Exception ('Invalid controller path: `' . $path . '`');
}
/*** set the path ***/
$this->path = $path;
}
/*** set the path to the controllers directory ***/
$router->setPath (__SITE_PATH . 'controller');
<?php
/**
*
* @load the controller
*
* @access public
*
* @return void
*
*/
public function loader()
{
/*** check the route ***/
$this->getController();
/*** if the file is not there diaf ***/
if (is_readable($this->file) == false)
{
echo $this->file;
die ('404 Not Found');
}
/*** include the controller ***/
include $this->file;
/*** a new controller class instance ***/
$class = $this->controller . 'Controller_';
$controller = new $class($this->registry);
/*** check if the action is callable ***/
if (is_callable(array($controller, $this->action)) == false)
{
$action = 'index';
}
else
{
$action = $this->action;
}
/*** run the action ***/
$controller->$action();
}
<?php
/**
*
* @get the controller
*
* @access private
*
* @return void
*
*/private function getController() {
/*** get the route from the url ***/
$route = (empty($_GET['rt'])) ? '' : $_GET['rt'];
if (empty($route))
{
$route = 'index';
}
else
{
/*** get the parts of the route ***/
$parts = explode('/', $route);
$this->controller = $parts[0];
if(isset( $parts[1]))
{
$this->action = $parts[1];
}
}
if (empty($this->controller))
{
$this->controller = 'index';
}
/*** Get action ***/
if (empty($this->action))
{
$this->action = 'index';
}
/*** set the file path ***/
$this->file = $this->path .'/'. $this->controller . '.php';
}?> The Controller
The Contoller is the C in MVC. The base controller is a simple abstract class that defines the structure of all controllers. By including the registry here, the registry is available to all class that extend from the base controller. An index() method has also been included in the base controller which means all controller classes that extend from it must have an index() method themselves. Add this code to the controller.class.php file in the application directory.
<?php
Abstract Class baseController {
/*
* @registry object
*/protected $registry;
function __construct($registry) {
$this->registry = $registry;
}
/**
* @all controllers must contain an index method
*/abstract function index();
}
?> http://www.example.com/blog
then the index method in the blog controller is called. A view method will also be created in the blog controller and when specified in the URL
http://www.example.com/blog/view
then the view method in the blog controller will be loaded. First lets see the index controller. This will reside in the controller directory.
<?php
class indexController extends baseController {
public function index() {
/*** set a template variable ***/
$this->registry->template->welcome = 'Welcome to PHPRO MVC';
/*** load the index template ***/
$this->registry->template->show('index');
}
}
?> The blogController class follows the same format but has has one small addition, a view() method. The view() method is an example of how a method other than the index() method may be called. The view method is loaded via the URL
http://www.example.com/blog/view
<?php
Class blogController Extends baseController {
public function index() {
$this->registry->template->blog_heading = 'This is the blog Index';
$this->registry->template->show('blog_index');
}
public function view(){
/*** should not have to call this here.... FIX ME ***/
$this->registry->template->blog_heading = 'This is the blog heading';
$this->registry->template->blog_content = 'This is the blog content';
$this->registry->template->show('blog_view');
}
}?> The View
The View, as you might have guessed, is the V in MVC. The View contains code that relates to presentation and presentation logic such as templating and caching. In the controller above we saw the show() method. This is the method that calls the view. The major component in the PHPRO MVC is the template class. The template.class.php file contains the class definition. Like the other classes, it has the registry available to it and also contains a __set() method in which template variables may be set and stored.The show method is the engine room of the view. This is the method that loads up the template itself, and makes the template variables available. Some larger MVC's will implement a template language that adds a further layer of abstraction from PHP. Added layers mean added overhead. Here we stick with the speed of PHP within the template, yet all the logic stays outside. This makes it easy for HTML monkies to create websites without any need to learn PHP or a template language. The template.class.php file looks like this:
<?php
Class Template {
/*
* @the registry
* @access private
*/private $registry;
/*
* @Variables array
* @access private
*/private $vars = array();
/**
*
* @constructor
*
* @access public
*
* @return void
*
*/function __construct($registry) {
$this->registry = $registry;
}
/**
*
* @set undefined vars
*
* @param string $index
*
* @param mixed $value
*
* @return void
*
*/
public function __set($index, $value)
{
$this->vars[$index] = $value;
}
function show($name) {
$path = __SITE_PATH . '/views' . '/' . $name . '.php';
if (file_exists($path) == false)
{
throw new Exception('Template not found in '. $path);
return false;
}
// Load variables
foreach ($this->vars as $key => $value)
{
$$key = $value;
}
include ($path);
}
}
?> Templates
The templates themselves are basically HTML files with a little PHP embedded. Do not let the separation Nazi's try to tell you that you need to have full seperation of HTML and PHP. Remember, PHP is an embeddable scripting language. This is the sort of task it is designed for and makes an efficient templating language. The template files belong in the views directory. Here is the index.php file.
<h1><?php echo $welcome; ?></h1>
<h1><?php echo $blog_heading; ?></h1>
<h1><?php echo $blog_heading; ?></h1>
<p><?php echo $blog_content; ?></p> 
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