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Service Objects

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I see Symfony as two big parts. The first half is the route, controller, response system. It's dead simple and well... you're already an expert on it! The second half of Symfony is all about the many useful objects that are floating around... just waiting for us to use them!

Hello Service Objects

For example, when we render a template, what we are actually doing is taking advantage of a Twig object and asking it to render a template. There's also a logger object, a cache object, a database connection object, an object that helps make API requests, and many, many more! And when you install a new bundle, that give you even more useful objects.

The truth is that everything that Symfony does is... actually done by one of these useful objects. Heck there's even a router object that's responsible for finding the matching route for the given page!

In the Symfony world, and really the object oriented programming world in general, these "objects that do work" have a special name: services. But don't let that word confuse you. When you hear service, just think: that's an object that does work! Like a templating object that renders a template or a database connection object that makes queries.

And since service objects do work, they're basically... tools that help you get your job done! The second half of Symfony is all about discovering which services are available and how to use them.

The debug:autowiring Command

Let's try something. In our controller, I want to log a message... maybe some debugging message. Since logging a message is work, it's done by a service. Does our app already have a logger service? And if so, how do we get it?

To find out, move over to your terminal and run another bin/console command:

php bin/console debug:autowiring

Say hello to one of the most powerful bin/console commands. I love this thing! This lists all of the services that exist in our app. Okay, it's actually not the full list, but this shows the services that you're most likely to need. And even though our app is small, there's a lot of stuff here! There's a filesystem service... and down here a cache service. There's even a twig service!

Is there a service for logging? You can look in this list... or you can re-run this command and search for the word log:

php bin/console debug:autowiring log

Excellent! For now, ignore everything except for the first line. This line tells us that there is a logger service and that this object implements an interface called Psr\Log\LoggerInterface.

Fetching a Service via Autowiring

Ok, so why does knowing that help us? Because if you want a service, you ask for it by using the type-hint shown in this command. It's called autowiring.

Let's try it. Head over to our controller and add a second argument. Actually, the order of these arguments doesn't matter. What matters is that the new argument is type-hinted with LoggerInterface. I'll hit tab to autocomplete that... so that PhpStorm adds the use statement on top.

In this case, the argument can be called anything, like $logger. When Symfony sees this type-hint, it looks inside of the debug:autowiring list... and because there's a match, it will pass us the logger service.

So we now know two different types of arguments that we are allowed to have in controller: you can have an argument whose name matches a wildcard in the route or an argument whose type-hint matches one of the services in our app.

Using the Logger

Ok, so now that we know Symfony will pass us the logger service object, let's use it! I don't know, yet, what methods I can call on it but... if we say $logger->... PhpStorm... tells us! That was easy!

I'm going to log something at an info() priority level. Let's say:

Returning API response for song

And then the $id.

... lines 3 - 4
use Psr\Log\LoggerInterface;
... lines 6 - 10
class SongController extends AbstractController
#[Route('/api/songs/{id<\d+>}', methods: ['GET'])]
public function getSong(int $id, LoggerInterface $logger): Response
... lines 16 - 22
$logger->info('Returning API response for song '.$id);
... lines 24 - 25

Actually, we can do something even cooler with this logger service. Add {song} to the message... and add a second argument, which is an array of extra information you want to attach to the log message. Pass song set to $id. In a minute, you'll see that the logger will print the actual id in place of {song}.

... lines 3 - 10
class SongController extends AbstractController
#[Route('/api/songs/{id<\d+>}', methods: ['GET'])]
public function getSong(int $id, LoggerInterface $logger): Response
... lines 16 - 22
$logger->info('Returning API response for song {song}', [
'song' => $id,
... lines 26 - 27

Anyways, this controller is for our API endpoint. So let's go over and refresh. Um... ok! So no error, that's good! But did it work? Where does the logger service... actually log to?

Let's find out next, learn a trick to see the profiler even for API requests and then leverage our second service directly.

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Refilon Avatar
Refilon Avatar Refilon | posted 1 year ago

Why not just do $logger->info("returning API response for song $id");?
It's the same and much more readable. You could use your method if you want to log an object or something maybe.


Hey Refilon,

Yea, you're right it's just simpler your way, but it was done that way for teaching purposes, you can use placeholders in your message and pass a $context array as second argument :)


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What PHP libraries does this tutorial use?

// composer.json
    "require": {
        "php": ">=8.0.2",
        "ext-ctype": "*",
        "ext-iconv": "*",
        "symfony/asset": "6.0.*", // v6.0.3
        "symfony/console": "6.0.*", // v6.0.3
        "symfony/dotenv": "6.0.*", // v6.0.3
        "symfony/flex": "^2", // v2.1.5
        "symfony/framework-bundle": "6.0.*", // v6.0.4
        "symfony/monolog-bundle": "^3.0", // v3.7.1
        "symfony/runtime": "6.0.*", // v6.0.3
        "symfony/twig-bundle": "6.0.*", // v6.0.3
        "symfony/ux-turbo": "^2.0", // v2.0.1
        "symfony/webpack-encore-bundle": "^1.13", // v1.13.2
        "symfony/yaml": "6.0.*", // v6.0.3
        "twig/extra-bundle": "^2.12|^3.0", // v3.3.8
        "twig/twig": "^2.12|^3.0" // v3.3.8
    "require-dev": {
        "symfony/debug-bundle": "6.0.*", // v6.0.3
        "symfony/stopwatch": "6.0.*", // v6.0.3
        "symfony/web-profiler-bundle": "6.0.*" // v6.0.3