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Let's talk about services.

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These are the most important concept in Symfony.

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And once you understand them,
honestly, you'll be able to do anything.

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First, a service is an object that does work.

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That's it.

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For example, if you instantiated a Logger object
that has a log() method, that's a service!

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It does work: it logs things!

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Or if you created a database connection object
that makes queries to the database then...

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yup! That's a service too.

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So then...

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if a service is just an object that does work...

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what lazy objects aren't services?

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Our Starship class is a perfect
example of a non service.

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It's main job is not to do
work: it's to hold data.

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Sure, it has a few public methods...

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and you could even put some logic
inside of these methods to do something.

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But ultimately, it's not a
worker, it's a data holder.

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What about controller classes?

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Yeah, they're services too.

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Their work is to create response objects.

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Anyway, every bit of work that's done in
Symfony is actually done by a service.

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Writing log messages to this file?

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Yeah, there's a service for that.

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Figuring out which route
matches the current URL?

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That's the router service!

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What about rendering a twig template?

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Yep, it turns out that the
render() method is a shortcut

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to find the correct service
object and call a method on it.

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You may sometimes also hear that
these services are organized

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into a big object called
the "service container".

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You can think of the container
like a giant associative array

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of service objects, each with a unique id.

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Want to see a list of every
service in our app right now?

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Me too! Find your terminal and run: bin/console
debug:container That's a lot of services!

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Let me make this smaller so
each fits on its own line...

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better. On the left side, we
see the ID of each service.

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And on the right, the class of the
object that the ID corresponds to.

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Cool, right?

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Go back to our controller and hold control or
command to open up the json() method again.

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Now this makes more sense!

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It's checking to see if the container
has a service whose ID is serializer.

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If it does, it grabs that
service from the container

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and calls the serialize() method on it.

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When we work with services, it
won't look exactly like this.

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But the super important thing is that
we now understand what's going on.

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My next question is: where
do these services come from?

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Like, who says there's a
service whose ID is twig...

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and that when we ask the container for it,
it should return a twig Environment object?

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The answer is: entirely from bundles.

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In fact, that's the main point
of installing a new bundle.

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Bundles give us services.

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Remember when we installed twig?

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It added a bundle to our app.

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And guess what that bundle did?

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Yup: it gave us new services,
including the twig service.

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Bundles give us services...

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and services are tools.

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And though there are many services in this list,

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the vast majority of these are low-level service
objects that we won't ever use or care about.

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We also won't care about the ID
of the services most of the time.

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Instead, run a related command called:

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php bin/console debug:autowiring This shows
us all the services that are autowireable,

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which is the technique that
we'll use to fetch services.

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It's basically a curated list of the
services that we're most likely to need.

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So let's do a challenge: let's
log something from our controller.

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Here's a sneak peek into
how I approach this problem

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in my brain: Ok, I need to log something!

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And... logging is work.

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And... services do work!

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Thus, there must be a logger
service that I can use!

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Quod erat demonstrandum!

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Forgive me latin nerds.

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The point is: if we want to log something,

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we just need to find the
service that does that work.

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Okay! Rerun the command but
search for log: Boom!

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It found about 10 services, all
starting with Psr\Log\LoggerInterface.

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We're going to talk about what these
other services are in the next tutorial.

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For now, focus on the main one.

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This tells me is that there is a
service in the container for a logger.

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And to get it, we can autowire
it using this interface.

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What does that mean?

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In the controller method where we want
the logger, add an argument type-hinted

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with LoggerInterface - hit
tab - then say $logger.

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In this case, the name of the argument
isn't important: it could be anything.

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What matters is that the LoggerInterface
- that corresponds to this use statement -

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matches the Psr\Log\LoggerInterface
from debug:autowiring.

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It's that simple!

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Symfony will see this type-hint and say: Oh!

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Since that type-hint matches the
autowiring type for this service,

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they must want me to pass
them that service object.

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I don't know why Symfony
sounds like a frog in my head.

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Anyway, let's see if this works.

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Add dd($logger): dd() stands for
"dump and die" and comes from Symfony.

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Refresh! Yes!

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It printed the object beautifully
then stopped execution.

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It's working!

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Symfony passes us a Monolog\Logger object,
which implements that LoggerInterface.

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The trick we just did - called
autowiring - works in exactly two places:

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our controller methods and the
__construct() method of any service.

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We'll see that second situation
in the next chapter.

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And if you're wondering where this Logger
service came from in the first place...

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we already know the answer!

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From a bundle.

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In this case, MonologBundle.

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And... how could we configure that service...

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to, I don't know, log to a different file?

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The answer is: config/packages/monolog.yaml.

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This config - including this line
- configures MonologBundle...

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which really means that it configures how
the services work that MonologBundle give us.

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We'll learn about this percent
syntax in the next tutorial,

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but this tells the Logger service
to log to this dev.log file.

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Ok, now that we have the
Logger service, let's use it!

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How? Well, of course, you can read the docs.

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But thanks to the type-hint,
our editor will help us!

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LoggerInterface has a bunch of methods.

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Let's use ->info() and say:
Starship collection retrieved.

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Try it out: refresh.

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The page worked...

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but did it log anything?

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We could go check the dev.log file.

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Or, we can use the Log section
of the profiler for this request.

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But... wait!

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This is an API request...

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so we don't have that cool web
debug toolbar on the bottom!

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That's true...

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but Symfony did still collect all that info!

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To get to the profiler for this
request, change the URL to /_profiler.

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This lists the most recent requests
to our app, with the newest on top.

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See this one?

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That's our API request from a minute ago!

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If you click this token...

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boom! We're looking at the profiler
for that API call in all its glory...

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including a Log section...

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with our message.

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Ok, now that we've seen how to use a
service, let's create our own service next!

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We're unstoppable!