Use the Symfony Binary to Create Symfony Applications

The Symfony binary is an executable command created in your machine when you download Symfony. It provides multiple utilities, including the simplest way to create new Symfony applications:

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$ symfony new my_project_directory

Under the hood, this Symfony binary command executes the needed Composer command to create a new Symfony application based on the current stable version.

Use the Default Directory Structure

Unless your project follows a development practice that imposes a certain directory structure, follow the default Symfony directory structure. It's flat, self-explanatory and not coupled to Symfony:

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your_project/
├─ assets/
├─ bin/
│  └─ console
├─ config/
│  ├─ packages/
│  └─ services.yaml
├─ migrations/
├─ public/
│  ├─ build/
│  └─ index.php
├─ src/
│  ├─ Kernel.php
│  ├─ Command/
│  ├─ Controller/
│  ├─ DataFixtures/
│  ├─ Entity/
│  ├─ EventSubscriber/
│  ├─ Form/
│  ├─ Repository/
│  ├─ Security/
│  └─ Twig/
├─ templates/
├─ tests/
├─ translations/
├─ var/
│  ├─ cache/
│  └─ log/
└─ vendor/

Use Environment Variables for Infrastructure Configuration

The values of these options change from one machine to another (e.g. from your development machine to the production server), but they don't modify the application behavior.

Use env vars in your project to define these options and create multiple .env files to configure env vars per environment.

Use Secrets for Sensitive Information

When your application has sensitive configuration, like an API key, you should store those securely via Symfony’s secrets management system.

Use Parameters for Application Configuration

These are the options used to modify the application behavior, such as the sender of email notifications, or the enabled feature toggles. Their value doesn't change per machine, so don't define them as environment variables.

Define these options as parameters in the config/services.yaml file. You can override these options per environment in the config/services_dev.yaml and config/services_prod.yaml files.

Use Short and Prefixed Parameter Names

Consider using app. as the prefix of your parameters to avoid collisions with Symfony and third-party bundles/libraries parameters. Then, use just one or two words to describe the purpose of the parameter:

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# config/services.yaml
parameters:
    # don't do this: 'dir' is too generic, and it doesn't convey any meaning
    app.dir: '...'
    # do this: short but easy to understand names
    app.contents_dir: '...'
    # it's OK to use dots, underscores, dashes or nothing, but always
    # be consistent and use the same format for all the parameters
    app.dir.contents: '...'
    app.contents-dir: '...'

Use Constants to Define Options that Rarely Change

Configuration options like the number of items to display in some listing rarely change. Instead of defining them as configuration parameters, define them as PHP constants in the related classes. Example:

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// src/Entity/Post.php
namespace App\Entity;

class Post
{
    public const NUMBER_OF_ITEMS = 10;

    // ...
}

The main advantage of constants is that you can use them everywhere, including Twig templates and Doctrine entities, whereas parameters are only available from places with access to the service container.

The only notable disadvantage of using constants for this kind of configuration values is that it's complicated to redefine their values in your tests.

Don't Create any Bundle to Organize your Application Logic

When Symfony 2.0 was released, applications used bundles to divide their code into logical features: UserBundle, ProductBundle, InvoiceBundle, etc. However, a bundle is meant to be something that can be reused as a stand-alone piece of software.

If you need to reuse some feature in your projects, create a bundle for it (in a private repository, do not make it publicly available). For the rest of your application code, use PHP namespaces to organize code instead of bundles.

Use Autowiring to Automate the Configuration of Application Services

Service autowiring is a feature that reads the type-hints on your constructor (or other methods) and automatically passes the correct services to each method, making it unnecessary to configure services explicitly and simplifying the application maintenance.

Use it in combination with service autoconfiguration to also add service tags to the services needing them, such as Twig extensions, event subscribers, etc.

Services Should be Private Whenever Possible

Make services private to prevent you from accessing those services via $container->get(). Instead, you will need to use proper dependency injection.

Use the YAML Format to Configure your own Services

If you use the default services.yaml configuration, most services will be configured automatically. However, in some edge cases you'll need to configure services (or parts of them) manually.

YAML is the format recommended configuring services because it's friendly to newcomers and concise, but Symfony also supports XML and PHP configuration.

Use Attributes to Define the Doctrine Entity Mapping

Doctrine entities are plain PHP objects that you store in some "database". Doctrine only knows about your entities through the mapping metadata configured for your model classes.

Doctrine supports several metadata formats, but it's recommended to use PHP attributes because they are by far the most convenient and agile way of setting up and looking for mapping information.

Make your Controller Extend the AbstractController Base Controller

Symfony provides a base controller which includes shortcuts for the most common needs such as rendering templates or checking security permissions.

Extending your controllers from this base controller couples your application to Symfony. Coupling is generally wrong, but it may be OK in this case because controllers shouldn't contain any business logic. Controllers should contain nothing more than a few lines of glue-code, so you are not coupling the important parts of your application.

Use Attributes or Annotations to Configure Routing, Caching, and Security

Using attributes or annotations for routing, caching, and security simplifies configuration. You don't need to browse several files created with different formats (YAML, XML, PHP): all the configuration is just where you require it, and it only uses one format.

Use Dependency Injection to Get Services

If you extend the base AbstractController, you can only get access to the most common services (e.g twig, router, doctrine, etc.), directly from the container via $this->container->get(). Instead, you must use dependency injection to fetch services by type-hinting action method arguments or constructor arguments.

Use Entity Value Resolvers If They Are Convenient

If you're using Doctrine, then you can optionally use the EntityValueResolver to automatically query for an entity and pass it as an argument to your controller. It will also show a 404 page if no entity can be found.

If the logic to get an entity from a route variable is more complex, instead of configuring the EntityValueResolver, it's better to make the Doctrine query inside the controller (e.g. by calling to a Doctrine repository method).

Use Snake Case for Template Names and Variables

Use lowercase snake_case for template names, directories, and variables (e.g. user_profile instead of userProfile and product/edit_form.html.twig instead of Product/EditForm.html.twig).

Prefix Template Fragments with an Underscore

Template fragments, also called "partial templates", allow to reuse template contents. Prefix their names with an underscore to better differentiate them from complete templates (e.g. _user_metadata.html.twig or _caution_message.html.twig).

Define your Forms as PHP Classes

Creating forms in classes allows reusing them in different parts of the application. Besides, not creating forms in controllers simplifies the code and maintenance of the controllers.

Add Form Buttons in Templates

Form classes should be agnostic to where they will be used. For example, the button of a form used to both create and edit items should change from "Add new" to "Save changes" depending on where it's used.

Instead of adding buttons in form classes or the controllers, it's recommended to add buttons in the templates. This also improves the separation of concerns because the button styling (CSS class and other attributes) is defined in the template instead of in a PHP class.

However, if you create a form with multiple submit buttons you should define them in the controller instead of the template. Otherwise, you won't be able to check which button was clicked when handling the form in the controller.

Define Validation Constraints on the Underlying Object

Attaching validation constraints to form fields instead of to the mapped object prevents the validation from being reused in other forms or other places where the object is used.

Use a Single Action to Render and Process the Form

Rendering forms and processing forms are two of the main tasks when handling forms. Both are too similar (most of the time, almost identical), so it's much simpler to let a single controller action handle both.

Use the XLIFF Format for Your Translation Files

Of all the translation formats supported by Symfony (PHP, Qt, .po, .mo, JSON, CSV, INI, etc.), XLIFF and gettext have the best support in the tools used by professional translators. And since it's based on XML, you can validate XLIFF file contents as you write them.

Symfony also supports notes in XLIFF files, making them more user-friendly for translators. At the end, good translations are all about context, and these XLIFF notes allow you to define that context.

Use Keys for Translations Instead of Content Strings

Using keys simplifies the management of the translation files because you can change the original contents in templates, controllers, and services without having to update all the translation files.

Keys should always describe their purpose and not their location. For example, if a form has a field with the label "Username", then a nice key would be label.username, not edit_form.label.username.

Define a Single Firewall

Unless you have two legitimately different authentication systems and users (e.g. form login for the main site and a token system for your API only), it's recommended to have only one firewall to keep things simple.

Additionally, you should use the anonymous key under your firewall. If you require users to be logged in for different sections of your site, use the access_control option.

Use the auto Password Hasher

The auto password hasher automatically selects the best possible encoder/hasher depending on your PHP installation. Currently, the default auto hasher is bcrypt.

Use Voters to Implement Fine-grained Security Restrictions

If your security logic is complex, you should create custom security voters instead of defining long expressions inside the #[Security] attribute.

Use Webpack Encore to Process Web Assets

Web assets are things like CSS, JavaScript, and image files that make the frontend of your site look and work great. Webpack is the leading JavaScript module bundler that compiles, transforms and packages assets for usage in a browser.

Webpack Encore is a JavaScript library that gets rid of most of Webpack complexity without hiding any of its features or distorting its usage and philosophy. It was created for Symfony applications, but it works for any application using any technology.

Smoke Test your URLs

In software engineering, smoke testing consists of "preliminary testing to reveal simple failures severe enough to reject a prospective software release". Using PHPUnit data providers you can define a functional test that checks that all application URLs load successfully:

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// tests/ApplicationAvailabilityFunctionalTest.php
namespace App\Tests;

use Symfony\Bundle\FrameworkBundle\Test\WebTestCase;

class ApplicationAvailabilityFunctionalTest extends WebTestCase
{
    /**
     * @dataProvider urlProvider
     */
    public function testPageIsSuccessful($url): void
    {
        $client = self::createClient();
        $client->request('GET', $url);

        $this->assertResponseIsSuccessful();
    }

    public function urlProvider(): \Generator
    {
        yield ['/'];
        yield ['/posts'];
        yield ['/post/fixture-post-1'];
        yield ['/blog/category/fixture-category'];
        yield ['/archives'];
        // ...
    }
}

Add this test while creating your application because it requires little effort and checks that none of your pages returns an error. Later, you'll add more specific tests for each page.

Hard-code URLs in a Functional Test

In Symfony applications, it's recommended to generate URLs using routes to automatically update all links when a URL changes. However, if a public URL changes, users won't be able to browse it unless you set up a redirection to the new URL.

That's why it's recommended to use raw URLs in tests instead of generating them from routes. Whenever a route changes, tests will fail, and you'll know that you must set up a redirection.