Loïc Faugeron Technical Blog

Learn Symfony2 - part 1: Composer 18/06/2014

Deprecated: This series has been re-written - see The Ultimate Developer Guide to Symfony

You don't know anything about the Symfony2 framework, and you'd like a quick guide to learn how to use it, and how it works?

Then this article is for you :) .

Don't get me wrong: one day or another you'll have to read the documentation, and you'll have to practice a lot in order to master it. But for now this guide should be a good start for you.

In the first article of this series, you'll learn about Composer, which helps you with third party library installation and updates.

Creating the project

In order to understand how Symfony2 works, we won't use the Symfony Standard Edition, but rather start from scratch with the bare minimum.

Let's create our project:

mkdir knight
cd knight
git init

Getting Composer

When developing a project the last thing you want is to waste your time re-inventing the wheel, so you install third party libraries. Those libraries have their own life cycle: they might release some bug fixes and new features after you installed them, so you'll need to update them sometimes.

Composer makes these things so easy you'll never have to worry again about versions. First download it:

curl -sS https://getcomposer.org/installer | php
sudo mv composer.phar /usr/local/bin/composer

And we're done! If only every project were so easy to install... :)

Installing and updating Symfony2

Actually, Symfony2 is only a name regrouping many libraries which can be used individually (you can even use them in other frameworks, CMS or projects like Drupal, phpBB, Laravel, eZ Publish, OroCRM and Piwik did).

Note: Symfony2 libraries are called components.

Composer was made to install libraries, so let's use it:

composer require 'symfony/symfony:~2.5' # install every single libraries in sf2

This command will do the following steps:

  1. create a composer.json configuration file if it doesn't already exist
  2. add symfony/symfony: ~2.5 in it (useful for further composer install)
  3. actually download symfony inside the vendor/symfony/symfony directory
  4. create a composer.lock file

Later on, to update those dependencies you'll just have to run composer update.

Note: a library on which you depend upon is called a dependency.

This will look in the composer.lock file to know which version has been installed (e.g. 2.5.0) and then checks if there's any new version available. For more information about how Composer handles versions, see Igor's article.

This means that you can totally ignore the vendor directory:

echo '/vendor/*' >> .gitignore

If your team wants to install your project, they'll just have to clone your repository and then run composer install which runs into the following steps:

  1. read the composer.json file to see the list of dependencies
  2. read the composer.lock file to check the version installed by the commiter
  3. download the dependencies with the version specified in the lock (even if new ones are available)

If a dependency is listed in composer.json but not in composer.lock, Composer will download the last matching version and add it to the lock.

This means that everyone will have the same version installed! If you allow only one person to run composer update you can guarantee this.


Because Composer knows where each classes of the installed libraries are, it provides a nice feature: autoloading.

Simply put, each time a class is called, Composer will automatically include the file where it's declared.

Your own code too can benefit from it. We just need to edit the composer.json file:

    "require": {
        "symfony/symfony": "~2.5"
    "autoload": {
        "psr-4": {
            "": "src/"

And run the following command to take the changes into account:

composer update

This tells Composer that we're going to follow the PSR-4 standard and that we're going to put our sources in the src directory.

Note: PSR 4 requires you to:

For example: the file src/Knight/ApplicationBundle/KnightApplicationBundle.php contains a class named KnightApplicationBundle located in the namespace Knight\ApplicationBundle.

Don't worry too much about it for now.


And that's everything you need to know about Composer for now. Let's commit our work:

git add -A
git commit -m 'Installed Symfony2'

I hope this could help you, stay tuned for the next articles!