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Zend Framework 2 Documentation (Manual)

File: /_sources/modules/zend.mvc.intro.txt

.. _zend.mvc.intro:

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.

.. _zend.mvc.intro.basic-application-structure:

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.

.. _zend.mvc.intro.basic-module-structure:

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.

.. code-block:: php
   :linenos:

   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:

.. table:: ``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.

.. _zend.mvc.intro.bootstrapping-an-application:

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:

.. code-block:: php
   :linenos:

   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.

.. code-block:: php
   :linenos:

   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();
   $application->run();

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.

.. code-block:: php
   :linenos:

   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.

.. _zend.mvc.intro.bootstrapping-a-modular-application:

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.

.. _zend.mvc.intro.bootstrapping-a-modular-application.configuring-the-module-manager:

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.

.. code-block:: php
   :linenos:

   <?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:

.. code-block:: php
   :linenos:

   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 :ref:`ModuleManager
documentation <zend.module-manager.intro>` goes into more detail on these.

.. _zend.mvc.intro.conclusion:

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.


.. _`Zend\\Mvc\\Application`: https://github.com/zendframework/zf2/blob/master/library/Zend/Mvc/Application.php
.. _`PSR-0 compliant directory structure`: https://github.com/php-fig/fig-standards/blob/master/accepted/PSR-0.md
.. _`PHPUnit`: http://phpunit.de