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Services

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It's time to talk about the most fundamental part of Symfony: services!

Honestly, Symfony is nothing more than a bunch of useful objects that work together. For example, there's a router object that matches routes and generates URLs. There's a Twig object that renders templates. And there's a Logger object that Symfony is already using internally to store things in a var/log/dev.log file.

Actually, everything in Symfony - I mean everything - is done by one of these useful objects. And these useful objects have a special name: services.

What's a Service?

But don't get too excited about that word - service. It's a special word for a really simple idea: a service is any object that does work, like generating URLs, sending emails or saving things to a database.

Symfony comes with a huge number of services, and I want you to think of services as your tools.

Like, if I gave you the logger service, or object, then you could use it to log messages. If I gave you a mailer service, you could send some emails! Tools!

The entire second half of Symfony is all about learning where to find these services and how to use them. Every time you learn about a new service, you get a new tool, and become just a little bit more dangerous!

Using the Logger Service

Let's check out the logging system. Find your terminal and run:

tail -f var/log/dev.log

I'll clear the screen. Now, refresh the page, and move back. Awesome! This proves that Symfony has some sort of logging system. And since everything is done by a service, there must be a logger object. So here's the question: how can we get the logger service so that we can log our own messages?

Here's the answer: inside the controller, on the method, add an additional argument. Give it a LoggerInterface type hint - hit tab to auto-complete that and call it whatever you want, how about $logger:

... lines 1 - 4
use Psr\Log\LoggerInterface;
... lines 6 - 10
class ArticleController extends AbstractController
{
... lines 13 - 41
public function toggleArticleHeart($slug, LoggerInterface $logger)
{
... lines 44 - 48
}
}

Remember: when you autocomplete, PhpStorm adds the use statement to the top for you.

Now, we can use one of its methods: $logger->info('Article is being hearted'):

... lines 1 - 10
class ArticleController extends AbstractController
{
... lines 13 - 41
public function toggleArticleHeart($slug, LoggerInterface $logger)
{
// TODO - actually heart/unheart the article!
$logger->info('Article is being hearted!');
... lines 47 - 48
}
}

Before we talk about this, let's try it! Find your browser and click the heart. That hit the AJAX endpoint. Go back to the terminal. Yes! There it is at the bottom. Hit Ctrl+C to exit tail.

Service Autowiring

Ok cool! But... how the heck did that work? Here's the deal: before Symfony executes our controller, it looks at each argument. For simple arguments like $slug, it passes us the wildcard value from the router:

... lines 1 - 10
class ArticleController extends AbstractController
{
... lines 13 - 38
/**
* @Route("/news/{slug}/heart", name="article_toggle_heart", methods={"POST"})
*/
public function toggleArticleHeart($slug, LoggerInterface $logger)
{
... lines 44 - 48
}
}

But for $logger, it looks at the type-hint and realizes that we want Symfony to pass us the logger object. Oh, and the order of the arguments does not matter.

This is a very powerful idea called autowiring: if you need a service object, you just need to know the correct type-hint to use! So... how the heck did I know to use LoggerInterface? Well, of course, if you look at the official Symfony docs about the logger, it'll tell you. But, there's a cooler way.

Go to your terminal and run:

./bin/console debug:autowiring

Boom! This is a full list of all of the type-hints that you can use to get a service. Notice that most of them say that they are an alias to something. Don't worry about that too much: like routes, each service has an internal name you can use to reference it. We'll learn more about that later. Oh, and whenever you install a new package, you'll get more and more services in this list. More tools!

Using Twig Directly

And check this out! If you want to get the Twig service, you can use either of these two type-hints.

And remember how I said that everything in Symfony is done by a service? Well, when we call $this->render() in a controller, that's just a shortcut to fetch the Twig service and call a method on it:

... lines 1 - 10
class ArticleController extends AbstractController
{
... lines 13 - 23
public function show($slug)
{
... lines 26 - 31
return $this->render('article/show.html.twig', [
... lines 33 - 35
]);
}
... lines 38 - 49
}

In fact, let's pretend that the $this->render() shortcut does not exist. How could we render a template? No problem: we just need the Twig service. Add a second argument with an Environment type-hint, because that's the class name we saw in debug:autowiring. Call the arg $twigEnvironment:

... lines 1 - 9
use Twig\Environment;
class ArticleController extends AbstractController
{
... lines 14 - 24
public function show($slug, Environment $twigEnvironment)
{
... lines 27 - 39
}
... lines 41 - 52
}

Next, change the return statement to be $html = $twigEnvironment->render():

... lines 1 - 9
use Twig\Environment;
class ArticleController extends AbstractController
{
... lines 14 - 24
public function show($slug, Environment $twigEnvironment)
{
... lines 27 - 32
$html = $twigEnvironment->render('article/show.html.twig', [
'title' => ucwords(str_replace('-', ' ', $slug)),
'slug' => $slug,
'comments' => $comments,
]);
... lines 38 - 39
}
... lines 41 - 52
}

The method we want to call on the Twig object is coincidentally the same as the controller shortcut.

Then at the bottom, return new Response() and pass $html:

... lines 1 - 8
use Symfony\Component\HttpFoundation\Response;
use Twig\Environment;
class ArticleController extends AbstractController
{
... lines 14 - 24
public function show($slug, Environment $twigEnvironment)
{
... lines 27 - 32
$html = $twigEnvironment->render('article/show.html.twig', [
'title' => ucwords(str_replace('-', ' ', $slug)),
'slug' => $slug,
'comments' => $comments,
]);
return new Response($html);
}
... lines 41 - 52
}

Ok, this is way more work than before... and I would not do this in a real project. But, I wanted to prove a point: when you use the $this->render() shortcut method on the controller, all it really does is call render() on the Twig service and then wrap it inside a Response object for you.

Try it! Go back and refresh the page. It works exactly like before! Of course we will use shortcut methods, because they make our life way more awesome. I'll change my code back to look like it did before. But the point is this: everything is done by a service. If you learn to master services, you can do anything from anywhere in Symfony.

There's a lot more to say about the topic of services, and so many other parts of Symfony: configuration, Doctrine & the database, forms, Security and APIs, to just name a few. The Space Bar is far from being the galactic information source that we know it will be!

But, congrats! You just spent an hour getting an awesome foundation in Symfony. You will not regret your hard work: you're on your way to building great things and, as always, becoming a better and better developer.

Alright guys, seeya next time!

Leave a comment!

What PHP libraries does this tutorial use?

// composer.json
{
    "require": {
        "php": "^7.1.3",
        "ext-iconv": "*",
        "sensio/framework-extra-bundle": "^5.1", // v5.1.3
        "symfony/asset": "^4.0", // v4.0.3
        "symfony/console": "^4.0", // v4.0.14
        "symfony/flex": "^1.0", // v1.2.7
        "symfony/framework-bundle": "^4.0", // v4.0.14
        "symfony/lts": "^4@dev", // dev-master
        "symfony/twig-bundle": "^4.0", // v4.0.3
        "symfony/web-server-bundle": "^4.0", // v4.0.3
        "symfony/yaml": "^4.0" // v4.0.14
    },
    "require-dev": {
        "easycorp/easy-log-handler": "^1.0.2", // v1.0.4
        "sensiolabs/security-checker": "^5.0", // v5.0.3
        "symfony/debug-bundle": "^3.3|^4.0", // v4.0.3
        "symfony/dotenv": "^4.0", // v4.0.14
        "symfony/monolog-bundle": "^3.0", // v3.1.2
        "symfony/phpunit-bridge": "^3.3|^4.0", // v4.0.3
        "symfony/profiler-pack": "^1.0", // v1.0.3
        "symfony/var-dumper": "^3.3|^4.0" // v4.0.3
    }
}