Setup, Services & the Service Container

Hey friends! Welcome back to Episode 2 of our Symfony 7 tutorial. I’ll be your brave - or maybe foolish guide through topics I absolutely love.. No matter what you do with Symfony, the most important thing you'll use are services - little yellow minions that do work in your app. We'll talk about configuration for those services as well as environments.

So what exactly is a service? That's easy! It's a plain PHP class that does work. For example, a Logger that helps you log messages is a service. Or a mailer that sends emails to your customers. Or a database connection object that you use to execute queries to the database. Those are all services. Even the controller that handles requests is a service, but it has super powers. We'll talk about that later.

Setup the Course Project

This course is titled "Fundamentals" because it's the foundation. Everything after this tutorial is just a variation of these themes. So, to code along with me, download the course code on this page, unzip it, and inside, you'll find a start/ directory with the same code that you see here. The README.md file has everything you need to get this application up and running. I've already completed most of these steps, so I'm going to move on to the last step and run the built-in Symfony web server. To do that, open your terminal and run:

symfony serve -d

The -d tells Symfony to start this in the background. You can find it at https://localhost:8000. I could copy and paste this in my browser, but I'm going to cheat. Hold "cmd" or "control" on a Mac, click this link, and... welcome back to Starshop, the site we created in Episode 1.

Services are everywhere

So, services are objects that do work: Logger, mailer, our database connection, and even our controllers. Is every object in our app a service? Actually no! We also have objects that hold data. For example, our Starship class isn't a service. It's just a plain data object. When we need these objects we just instantiate them the normal boring way.

But services - objects that do work - are different. We could instantiate them manually, but in practice, some thing else handles that: the service container. It's a huge fan of our services. It knows everything about them, from the class name, to every constructor argument. If you ask it for a service, it will instantiate it for you and return a ready-to-use PHP object. And it's smart if you request a service multiple times, only creates it once. For example, our app only needs one logger. If you ask for the logger 5 times, it's created just once then that same object is returned every time!

Okay, so... how do we know which services we have? To see the list of all of the services we have available, we're going to use a special command. Over at your terminal, run:

bin/console debug:container

Hello Bundles

Here you can see a long list of services we can use in our app. But where are these coming from? Who tells the container there should be a logger service whose class is Logger and it should be instantiated with these arguments? Some services are from our code and we'll talk about how those are registered in a bit. But the vast majority comes from bundles. Bundles are just plugins you can add to Symfony applications. They provide a few things, but the most important is services. Each bundle has a config file that says:

Hey! I want to have a service called logger which should be an instance of "Logger", and it should be instantiated with these arguments.

So services are tools and bundles give us tools. Over in our code, open config/bundles.php. This is the file that's responsible for registering bundles in our application. And check it out! We already have ten of them! Some of these, like WebProfilerBundle, are only available for a specific environment. MonologBundle is what provides the Logger service we're using in StartshipRepository when we log a message. Or, if we delete this TwigBundle line completely, the render() method we're calling in our controllers won't work anymore. That's because, behind the scenes, this is using the twig service to render templates. More on that later.

Next, let's talk about how to install new bundles in your application to get new services.