The Architecture

Understanding the Directory Structure

The directory structure of a Symfony application is rather flexible, but the recommended structure is as follows:

app/

The application configuration, templates and translations.

src/

The project's PHP code.

vendor/

The third-party dependencies.

web/

The web root directory.

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// web/app.php
require_once __DIR__.'/../app/bootstrap.php.cache';
require_once __DIR__.'/../app/AppKernel.php';

use Symfony\Component\HttpFoundation\Request;

$kernel = new AppKernel('prod', false);
$kernel->loadClassCache();
$request = Request::createFromGlobals();
$response = $kernel->handle($request);
$response->send();

Understanding the Bundle System

This section introduces one of the greatest and most powerful features of Symfony: The bundle system.

A bundle is kind of like a plugin in other software. So why is it called a bundle and not a plugin? This is because everything is a bundle in Symfony, from the core framework features to the code you write for your application.

All the code you write for your application is organized in bundles. In Symfony speak, a bundle is a structured set of files (PHP files, stylesheets, JavaScripts, images, ...) that implements a single feature (a blog, a forum, ...) and which can be easily shared with other developers.

Bundles are first-class citizens in Symfony. This gives you the flexibility to use pre-built features packaged in third-party bundles or to distribute your own bundles. It makes it easy to pick and choose which features to enable in your application and optimize them the way you want. And at the end of the day, your application code is just as important as the core framework itself.

Symfony already includes an AppBundle that you may use to start developing your application. Then, if you need to split the application into reusable components, you can create your own bundles.

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// app/AppKernel.php
public function registerBundles()
{
    $bundles = array(
        new Symfony\Bundle\FrameworkBundle\FrameworkBundle(),
        new Symfony\Bundle\SecurityBundle\SecurityBundle(),
        new Symfony\Bundle\TwigBundle\TwigBundle(),
        new Symfony\Bundle\MonologBundle\MonologBundle(),
        new Symfony\Bundle\SwiftmailerBundle\SwiftmailerBundle(),
        new Symfony\Bundle\DoctrineBundle\DoctrineBundle(),
        new Symfony\Bundle\AsseticBundle\AsseticBundle(),
        new Sensio\Bundle\FrameworkExtraBundle\SensioFrameworkExtraBundle(),
        new AppBundle\AppBundle(),
    );

    if (in_array($this->getEnvironment(), array('dev', 'test'))) {
        $bundles[] = new Symfony\Bundle\WebProfilerBundle\WebProfilerBundle();
        $bundles[] = new Sensio\Bundle\DistributionBundle\SensioDistributionBundle();
        $bundles[] = new Sensio\Bundle\GeneratorBundle\SensioGeneratorBundle();
    }

    return $bundles;
}

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# app/config/config.yml
imports:
    - { resource: parameters.yml }
    - { resource: security.yml }
    - { resource: services.yml }

framework:
    #esi:             ~
    #translator:      { fallbacks: ['%locale%'] }
    secret:          '%secret%'
    router:
        resource: '%kernel.root_dir%/config/routing.yml'
        strict_requirements: '%kernel.debug%'
    form:            true
    csrf_protection: true
    validation:      { enable_annotations: true }
    templating:      { engines: ['twig'] }
    default_locale:  '%locale%'
    trusted_proxies: ~
    session:         ~

# Twig Configuration
twig:
    debug:            '%kernel.debug%'
    strict_variables: '%kernel.debug%'

# Swift Mailer Configuration
swiftmailer:
    transport: '%mailer_transport%'
    host:      '%mailer_host%'
    username:  '%mailer_user%'
    password:  '%mailer_password%'
    spool:     { type: memory }

# ...

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# app/config/config_dev.yml
imports:
    - { resource: config.yml }

framework:
    router:   { resource: '%kernel.root_dir%/config/routing_dev.yml' }
    profiler: { only_exceptions: false }

web_profiler:
    toolbar: true
    intercept_redirects: false

# ...

Using Vendors

Odds are that your application will depend on third-party libraries. Those should be stored in the vendor/ directory. You should never touch anything in this directory, because it is exclusively managed by Composer. This directory already contains the Symfony libraries, the SwiftMailer library, the Doctrine ORM, the Twig templating system and some other third party libraries and bundles.

Understanding the Cache and Logs

Symfony applications can contain several configuration files defined in several formats (YAML, XML, PHP, etc.). Instead of parsing and combining all those files for each request, Symfony uses its own cache system. In fact, the application configuration is only parsed for the very first request and then compiled down to plain PHP code stored in the app/cache/ directory.

In the development environment, Symfony is smart enough to update the cache when you change a file. But in the production environment, to speed things up, it is your responsibility to clear the cache when you update your code or change its configuration. Execute this command to clear the cache in the prod environment:

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$ php app/console cache:clear --env=prod

When developing a web application, things can go wrong in many ways. The log files in the app/logs/ directory tell you everything about the requests and help you fix the problem quickly.

Using the Command Line Interface

Each application comes with a command line interface tool (app/console) that helps you maintain your application. It provides commands that boost your productivity by automating tedious and repetitive tasks.

Run it without any arguments to learn more about its capabilities:

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$ php app/console

The --help option helps you discover the usage of a command:

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$ php app/console debug:router --help

Final Thoughts

Call me crazy, but after reading this part, you should be comfortable with moving things around and making Symfony work for you. Everything in Symfony is designed to get out of your way. So, feel free to rename and move directories around as you see fit.

And that's all for the quick tour. From testing to sending emails, you still need to learn a lot to become a Symfony master. Ready to dig into these topics now? Look no further - go to the official Symfony Documentation and pick any topic you want.