I actually wrote about this recently in an article about OroCRM, which is based on Symfony 2. If you want some of the context/why of the different commands, you might find it interesting.
There are two different systems for including frontend files (javascript, css, images, etc.) in a Symfony application. The assets:install command came first. This command will search all the Symfony Bundles in an application for a
Resources/public
folder. If found, the assets:install command will copy or symlink files from Resources/public to web/public/bundle/[bundle-name]. This is where links created with the twig assets function will look for these files. This
<script src="{{ asset('js/script.js') }}" type="text/javascript"></script>
Becomes this
<script src="/bundles/[bundle-name]/js/script.js" type="text/javascript"></script>
That's all the assets system does. It lets you store your frontend files with the bundle.
The assetic system is different. With assetic, you link to files like this.
{% javascripts '@AcmeFooBundle/Resources/public/js/foo.js' %}
<script type="text/javascript" src="{{ asset_url }}"></script>
{% endjavascripts %}
There's similar tags for stylesheets and images. Notice that assetic allows you to link to files in any bundle. (@AcmeFooBundle). Assetic will also let you link to multiple files in a folder with a wildcard.
{% javascripts '@AcmeFooBundle/Resources/public/js/*' %}
<script type="text/javascript" src="{{ asset_url }}"></script>
{% endjavascripts %}
Another difference with assetic is in the links generated. In the dev environment they'll look something like this.
<script type="text/javascript" src="/app_dev.php/js/foo.js"></script>
<script type="text/javascript" src="/app_dev.php/js/bar.js"></script>
That is, requests for these files will run through the PHP front controller (app_dev.php) via special routes setup in the assetic bundle. This means, when you're in dev mode, you never need to dump you assets. They're included automatically. It also allows you to apply filters to the files. For example, the following applies the cssrewrite filter to the files pulled in.
{% stylesheets 'bundles/acme_foo/css/*' filter='cssrewrite' %}
<link rel="stylesheet" href="{{ asset_url }}" />
{% endstylesheets %}
If you ever wanted to programmatically alter the output of your frontend assets —?assetic lets you do that by writing custom twig filters.
However, this is performance intensive. In production, instead of linking each file individually via a the PHP front controller file, the generated HTML will look like this
<script type="text/javascript" src="/js/as5s31l.js"></script>
Where does as5s31l.js come from? That's what the assetic:dump command does. It combines all the individual javascript/css files (after applying the filters) and creates a nice, static, cacheable file for production.
What You Need to Do
Unless the project specifically tells you otherwise, you should always run assets:install and assetic:dump, because you'll never know which of your third party bundles use these commands. You only need to run assetic:dump before you deploy or view the application in prod mode. Order is irrelevant.
As for which system your bundle should use —?if you've read the above and you're unsure what assetic can do for you, use assets. You'll be fine.
