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Symfony is really two parts...

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and we've already learned one of them.

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The first part is the route
and controller system.

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And I hope you're feeling pretty
comfortable: create a route,

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it executes a controller
function, we return a response.

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The second half of Symfony is all
about the many "useful objects"

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that are floating around inside Symfony.

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For example, when we render a template, what
we're actually doing is taking advantage

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of a twig object and asking it to render.

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The render() method is just a
shortcut to use that object.

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There is also a logger object, a cache object
and many more, like a database connection object

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and an object that helps make
HTTP requests to other APIs.

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Basically...

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every single thing that Symfony
does - or that we do -

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is actually done by one of these useful objects.

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Heck, even the router is an object that figures
out which route matches the current request.

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In the Symfony world - well, really, in
the object-oriented programming world -

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these "objects that do work" are
given a special name: services.

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But don't let that confuse you: when
you hear "service", just think: Hey!

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That's an object that does some
work - like a logger object

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or a database object that makes queries.

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Inside CommentController, let's log something.

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To do that work, we need the "logger" service.

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How can we get it?

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Find your terminal and run: php bin/console
debug:autowiring Say hello to one

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of the most important bin/console commands.

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This gives us a list of all
the service objects in our app.

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Well, ok, this isn't all of
them: but it is a full list

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of all the services that you are likely to need.

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Even in our small app, there's
a lot of stuff in here:

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there's something called
Psr\Log\LoggerInterface,

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there's stuff for caching and plenty more.

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As we install more bundles, this list will grow.

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More services, means more tools.

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To find which service allows
us to "log" things, run:

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php bin/console debug:autowiring log
This returns a bunch of things...

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but ignore all of these down here
for now and focus on the top line.

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This tells us that there
is a logger service object

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and its class implements
some Psr\Log\LoggerInterface.

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Why is that important?

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Because if you want the logger service,
you ask for it by using this type-hint.

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It's called "autowiring".

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Here's how you get a service
from inside a controller.

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Add a third argument to your method -
though the argument order doesn't matter.

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Say LoggerInterface - auto-complete the one
from Psr\Log\LoggerInterface - and $logger.

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This added a use statement above the
class for Psr\Log\LoggerInterface,

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which matches the type-hint that
debug:autowiring told us to use.

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Thanks to this type-hint, when
Symfony renders our controller,

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it will know that we want the logger
service to be passed to this argument.

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So... yea: there are now two types of arguments
that you can add to your controller method.

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First, you can have an argument whose
name matches a wildcard in your route.

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And second, you can have an argument
whose type-hint matches one of the class

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or interface names listed in debug:autowiring.

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CacheInterface is another type-hint
we could use to get a caching service.

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So... let's use this object!

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What methods can we call on it?

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I have no idea!

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But because we properly type-hinted
the argument, we can say $logger->

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and PhpStorm tells us exactly
what methods it has.

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Let's use $logger->info() to say "Voting up!".

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Copy that and say "Voting down!"

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on the else.

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Testing time!

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Refresh the page and...

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let's click up, down, up.

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It... at least doesn't look broken.

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Hover over the AJAX part
of the web debug toolbar

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and open the profiler for one of these requests.

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The profiler has a "Logs"
section , which is the easiest way

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to see the log entries for a single request.

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There it is!

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"Voting up!".

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You could also find this in
the var/log/dev.log file.

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The point is: Symfony has many, many
useful objects, I mean "services".

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And little-by-little, we're going
to start using more of them...

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each time by adding a type-hint to
tell Symfony which service we need.

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Let's look at one other example.

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The first service that we used
in our code was the Twig service.

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We used it...

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kind of "indirectly" by saying $this->render().

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In reality, that method is a shortcut to
use the Twig service behind the scenes.

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And that should not surprise you.

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Like I said, everything that's done in
Symfony is actually done by a service.

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As a challenge, let's pretend that
the render() function doesn't exist.

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Gasp! In the homepage() controller,
comment-out the render() line.

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So... how can we use the Twig service
directly to render a template?

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I don't know!

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We could definitely find some
documentation about this...

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but let's see if we can figure
it out by ourselves with the help

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of the debug:autowiring command: php
bin/console debug:autowiring twig And, voilà!

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There is apparently a class called
Twig\Environment that we can use

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as a "type-hint" to get a Twig service.

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In our controller, add Environment and
hit tab to add the use statement on top.

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I'll call the argument $twigEnvironment.

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Inside, add $html = $twigEnvironment->.

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Once again, without reading any documentation,
thanks to the fact that we're coding responsibly

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and using type-hints, PhpStorm shows
us all the methods on this class.

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Hey! This render() method looks
like it might be what we need!

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Pass the same template name as before.

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When you use twig directly, instead
of returning a Response object,

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it returns a string with the HTML.

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No problem: finish with return new Response()
- the one from HttpFoundation - and pass $html.

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This is now doing the exact
same thing as $this->render().

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To prove it, click the homepage link.

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It still works.

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Now in reality, other than being a
"great exercise" to understand services,

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there's no reason to do this the long way.

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I just want you to understand
that services are really the

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"things" doing the work behind the scenes.

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And if you want to do something - like log or
render a template - what you really need is

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to find out which service does that work.

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Trust me, this is the key to unlocking
your full potential in Symfony.

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Let's put the old, shorter code back,
and comment out the longer example.

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Ok, you've almost made it through
the first Symfony tutorial.

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You rock! As a reward, we're going
to finish with something fun:

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an introduction into a system called
Webpack Encore that will allow you

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to do crazy things with your CSS and JavaScript.