Introduction to the MVC Layer

Zend\Mvc is a brand new MVC implementation designed from the ground up for Zend Framework 2, focusing on performance and flexibility.

The MVC layer is built on top of the following components:

• Zend\ServiceManager - Zend Framework provides a set of default service definitions set up at Zend\Mvc\Service. The ServiceManager creates and configures your application instance and workflow.
• Zend\EventManager - The MVC is event driven. This component is used everywhere from initial bootstrapping of the application, through returning response and request calls, to setting and retrieving routes and matched routes, as well as render views.
• Zend\Http - specifically the request and response objects, used within:
• Zend\Stdlib\DispatchableInterface. All “controllers” are simply dispatchable objects.

Within the MVC layer, several sub-components are exposed:

• Zend\Mvc\Router contains classes pertaining to routing a request. In other words, it matches the request to its respective controller (or dispatchable).
• Zend\Http\PhpEnvironment provides a set of decorators for the HTTP Request and Response objects that ensure the request is injected with the current environment (including query parameters, POST parameters, HTTP headers, etc.)
• Zend\Mvc\Controller, a set of abstract “controller” classes with basic responsibilities such as event wiring, action dispatching, etc.
• Zend\Mvc\Service provides a set of ServiceManager factories and definitions for the default application workflow.
• Zend\Mvc\View provides default wiring for renderer selection, view script resolution, helper registration, and more; additionally, it provides a number of listeners that tie into the MVC workflow, providing features such as automated template name resolution, automated view model creation and injection, and more.

The gateway to the MVC is the Zend\Mvc\Application object (referred to as Application henceforth). Its primary responsibilities are to bootstrap resources, route the request, and to retrieve and dispatch the controller matched during routing. Once accomplished, it will render the view, and finish the request, returning and sending the response.

Basic Application Structure

The basic application structure follows:

application_root/
    config/
        application.config.php
        autoload/
            global.php
            local.php
            // etc.
    data/
    module/
    vendor/
    public/
        .htaccess
        index.php
    init_autoloader.php

The public/index.php marshalls all user requests to your website, retrieving an array of configuration located in config/application.config.php. On return, it run()s the Application, processing the request and returning a response to the user.

The config directory as described above contains configuration used by the Zend\ModuleManager to load modules and merge configuration (e.g., database configuration and credentials); we will detail this more later.

The vendor sub-directory should contain any third-party modules or libraries on which your application depends. This might include Zend Framework, custom libraries from your organization, or other third-party libraries from other projects. Libraries and modules placed in the vendor sub-directory should not be modified from their original, distributed state.

Finally, the module directory will contain one or more modules delivering your application’s functionality.

Let’s now turn to modules, as they are the basic units of a web application.

Basic Module Structure

A module may contain anything: PHP code, including MVC functionality; library code; view scripts; and/or or public assets such as images, CSS, and JavaScript. The only requirement – and even this is optional – is that a module acts as a PHP namespace and that it contains a Module.php class under that namespace. This class is eventually consumed by Zend\ModuleManager to perform a number of tasks.

The recommended module structure follows:

module_root<named-after-module-namespace>/
    Module.php
    autoload_classmap.php
    autoload_function.php
    autoload_register.php
    config/
        module.config.php
    public/
        images/
        css/
        js/
    src/
        <module_namespace>/
            <code files>
    test/
        phpunit.xml
        bootstrap.php
        <module_namespace>/
            <test code files>
    view/
        <dir-named-after-module-namespace>/
            <dir-named-after-a-controller>/
                <.phtml files>

Since a module acts as a namespace, the module root directory should be that namespace. This namespace could also include a vendor prefix of sorts. As an example a module centered around “User” functionality delivered by Zend might be named “ZendUser”, and this is also what the module root directory will be named.

The Module.php file directly under the module root directory will be in the module namespace shown below.

namespace ZendUser;

class Module
{
}

When an init() method is defined, this method will be triggered by a Zend\ModuleManager listener when it loads the module class, and passed an instance of the manager by default. This allows you to perform tasks such as setting up module-specific event listeners. But be cautious, the init() method is called for every module on every page request and should only be used for performing lightweight tasks such as registering event listeners. Similarly, an onBootstrap() method (which accepts an MvcEvent instance) may be defined; it is also triggered for every page request, and should be used for lightweight tasks as well.

The three autoload_*.php files are not required, but recommended. They provide the following:

autoload_*.php Files

File	Description
autoload_classmap.php	Should return an array classmap of class name/filename pairs (with the filenames resolved via the __DIR__ magic constant).
autoload_function.php	Should return a PHP callback that can be passed to spl_autoload_register(). Typically, this callback should utilize the map returned by autoload_classmap.php.
autoload_register.php	should register a PHP callback (is typically returned by autoload_function.php with spl_autoload_register().

The point of these three files is to provide reasonable default mechanisms for autoloading the classes contained in the module, thus providing a trivial way to consume the module without requiring Zend\ModuleManager (e.g., for use outside a ZF2 application).

The config directory should contain any module-specific configuration. These files may be in any format Zend\Config supports. We recommend naming the main configuration “module.format”, and for PHP-based configuration, “module.config.php”. Typically, you will create configuration for the router as well as for the dependency injector.

The src directory should be a PSR-0 compliant directory structure with your module’s source code. Typically, you should at least have one sub-directory named after your module namespace; however, you can ship code from multiple namespaces if desired.

The test directory should contain your unit tests. Typically, these are written using PHPUnit, and contain artifacts related to its configuration (e.g., phpunit.xml, bootstrap.php).

The public directory can be used for assets that you may want to expose in your application’s document root. These might include images, CSS files, JavaScript files, etc. How these are exposed is left to the developer.

The view directory contains view scripts related to your controllers.

Bootstrapping an Application

The Application has six basic dependencies.

• configuration, usually an array or object implementing Traversable.
• ServiceManager instance.
• EventManager instance, which, by default, is pulled from the ServiceManager, by the service name “EventManager”.
• ModuleManager instance, which, by default, is pulled from the ServiceManager, by the service name “ModuleManager”.
• Request instance, which, by default, is pulled from the ServiceManager, by the service name “Request”.
• Response instance, which, by default, is pulled from the ServiceManager, by the service name “Response”.

These may be satisfied at instantiation:

use Zend\EventManager\EventManager;
use Zend\Http\PhpEnvironment;
use Zend\ModuleManager\ModuleManager;
use Zend\Mvc\Application;
use Zend\ServiceManager\ServiceManager;

$config = include 'config/application.config.php';

$serviceManager = new ServiceManager();
$serviceManager->setService('EventManager', new EventManager());
$serviceManager->setService('ModuleManager', new ModuleManager($config));
$serviceManager->setService('Request', new PhpEnvironment\Request());
$serviceManager->setService('Response', new PhpEnvironment\Response());

$application = new Application($config, $serviceManager);

Once you’ve done this, there are two additional actions you can take. The first is to “bootstrap” the application. In the default implementation, this does the following:

• Attaches the default route listener (Zend\Mvc\RouteListener).
• Attaches the default dispatch listener (Zend\Mvc\DispatchListener).
• Attaches the ViewManager listener (Zend\Mvc\View\ViewManager).
• Creates the MvcEvent, and injects it with the application, request, and response; it also retrieves the router (Zend\Mvc\Router\Http\TreeRouteStack) at this time and attaches it to the event.
• Triggers the “bootstrap” event.

If you do not want these actions, or want to provide alternatives, you can do so by extending the Application class and/or simply coding what actions you want to occur.

The second action you can take with the configured Application is to run() it. Calling this method simply does the following: it triggers the “route” event, followed by the “dispatch” event, and, depending on execution, the “render” event; when done, it triggers the “finish” event, and then returns the response instance. If an error occurs during either the “route” or “dispatch” event, a “dispatch.error” event is triggered as well.

This is a lot to remember in order to bootstrap the application; in fact, we haven’t covered all the services available by default yet. You can greatly simplify things by using the default ServiceManager configuration shipped with the MVC.

use Zend\Loader\AutoloaderFactory;
use Zend\Mvc\Service\ServiceManagerConfig;
use Zend\ServiceManager\ServiceManager;

// setup autoloader
AutoloaderFactory::factory();

// get application stack configuration
$configuration = include 'config/application.config.php';

// setup service manager
$serviceManager = new ServiceManager(new ServiceManagerConfig());
$serviceManager->setService('ApplicationConfig', $configuration);

// load modules -- which will provide services, configuration, and more
$serviceManager->get('ModuleManager')->loadModules();

// bootstrap and run application
$application = $serviceManager->get('Application');
$application->bootstrap();
$response = $application->run();
$response->send();

You can make this even simpler by using the init() method of the Application. This is a static method for quick and easy initialization of the Application.

use Zend\Loader\AutoloaderFactory;
use Zend\Mvc\Application;
use Zend\Mvc\Service\ServiceManagerConfig;
use Zend\ServiceManager\ServiceManager;

// setup autoloader
AutoloaderFactory::factory();

// get application stack configuration
$configuration = include 'config/application.config.php';

// The init() method does something very similar with the previous example.
Application::init($configuration)->run();

The init() method will basically do the following:

• Grabs the application configuration and pulls from the service_manager key, creating a ServiceManager

  instance with it and with the default services shipped with Zend\Mvc;

• Create a service named ApplicationConfig with the application configuration array;

• Grabs the ModuleManager service and load the modules;

• bootstrap()s the Application and returns its instance;

Note

If you use the init() method, you cannot specify a service with the name of ‘ApplicationConfig’ in your service manager config. This name is reserved to hold the array from application.config.php.

The following services can only be overridden from application.config.php:

• ModuleManager
• SharedEventManager
• EventManager & Zend\EventManager\EventManagerInterface

All other services are configured after module loading, thus can be overridden by modules.

You’ll note that you have a great amount of control over the workflow. Using the ServiceManager, you have fine-grained control over what services are available, how they are instantiated, and what dependencies are injected into them. Using the EventManager‘s priority system, you can intercept any of the application events (“bootstrap”, “route”, “dispatch”, “dispatch.error”, “render”, and “finish”) anywhere during execution, allowing you to craft your own application workflows as needed.

Bootstrapping a Modular Application

While the previous approach largely works, where does the configuration come from? When we create a modular application, the assumption will be that it’s from the modules themselves. How do we get that information and aggregate it, then?

The answer is via Zend\ModuleManager\ModuleManager. This component allows you to specify where modules exist. Then, it will locate each module and initialize it. Module classes can tie into various listeners on the ModuleManager in order to provide configuration, services, listeners, and more to the application. Sounds complicated? It’s not.

Configuring the Module Manager

The first step is configuring the module manager. Simply inform the module manager which modules to load, and potentially provide configuration for the module listeners.

Remember the application.config.php from earlier? We’re going to provide some configuration.

<?php
// config/application.config.php
return array(
    'modules' => array(
        /* ... */
    ),
    'module_listener_options' => array(
        'module_paths' => array(
            './module',
            './vendor',
        ),
    ),
);

As we add modules to the system, we’ll add items to the modules array.

Each Module class that has configuration it wants the Application to know about should define a getConfig() method. That method should return an array or Traversable object such as Zend\Config\Config. As an example:

namespace ZendUser;

class Module
{
    public function getConfig()
    {
        return include __DIR__ . '/config/module.config.php'
    }
}

There are a number of other methods you can define for tasks ranging from providing autoloader configuration, to providing services to the ServiceManager, to listening to the bootstrap event. The ModuleManager documentation goes into more detail on these.

Conclusion

The ZF2 MVC layer is incredibly flexible, offering an opt-in, easy to create modular infrastructure, as well as the ability to craft your own application workflows via the ServiceManager and EventManager. The ModuleManager is a lightweight and simple approach to enforcing a modular architecture that encourages clean separation of concerns and code re-use.