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Organizing Your Business Logic

Organizing Your Business Logic

In computer software, business logic or domain logic is "the part of the program that encodes the real-world business rules that determine how data can be created, displayed, stored, and changed" (read full definition).

In Symfony applications, business logic is all the custom code you write for your app that's not specific to the framework (e.g. routing and controllers). Domain classes, Doctrine entities and regular PHP classes that are used as services are good examples of business logic.

For most projects, you should store all your code inside the src/ directory. Inside here, you can create whatever directories you want to organize things:

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symfony-project/
├─ config/
├─ public/
├─ src/
│  └─ Utils/
│     └─ MyClass.php
├─ tests/
├─ var/
└─ vendor/

Services: Naming and Configuration

Best Practice

Best Practice

Use autowiring to automate the configuration of application services.

Service autowiring is a feature provided by Symfony's Service Container to manage services with minimal configuration. It reads the type-hints on your constructor (or other methods) and automatically passes the correct services to each method. It can also add service tags to the services needed them, such as Twig extensions, event subscribers, etc.

The blog application needs a utility that can transform a post title (e.g. "Hello World") into a slug (e.g. "hello-world") to include it as part of the post URL. Let's create a new Slugger class inside src/Utils/:

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// src/Utils/Slugger.php
namespace App\Utils;

class Slugger
{
    public function slugify(string $value): string
    {
        // ...
    }
}

If you're using the default services.yaml configuration, this class is auto-registered as a service whose ID is App\Utils\Slugger (or simply Slugger::class if the class is already imported in your code).

Best Practice

Best Practice

The id of your application's services should be equal to their class name, except when you have multiple services configured for the same class (in that case, use a snake case id).

Now you can use the custom slugger in any other service or controller class, such as the AdminController:

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use App\Utils\Slugger;

public function create(Request $request, Slugger $slugger)
{
    // ...

    if ($form->isSubmitted() && $form->isValid()) {
        $slug = $slugger->slugify($post->getTitle());
        $post->setSlug($slug);

        // ...
    }
}

Services can also be public or private. If you use the default services.yaml configuration, all services are private by default.

Best Practice

Best Practice

Services should be private whenever possible. This will prevent you from accessing that service via $container->get(). Instead, you will need to use dependency injection.

Service Format: YAML

In the previous section, YAML was used to define the service.

Best Practice

Best Practice

Use the YAML format to define your own services.

This is controversial, and in our experience, YAML and XML usage is evenly distributed among developers, with a slight preference towards YAML. Both formats have the same performance, so this is ultimately a matter of personal taste.

We recommend YAML because it's friendly to newcomers and concise. You can of course use whatever format you like.

Using a Persistence Layer

Symfony is an HTTP framework that only cares about generating an HTTP response for each HTTP request. That's why Symfony doesn't provide a way to talk to a persistence layer (e.g. database, external API). You can choose whatever library or strategy you want for this.

In practice, many Symfony applications rely on the independent Doctrine project to define their model using entities and repositories. Just like with business logic, we recommend storing Doctrine entities in the src/Entity/ directory.

The three entities defined by our sample blog application are a good example:

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symfony-project/
├─ ...
└─ src/
   └─ Entity/
      ├─ Comment.php
      ├─ Post.php
      └─ User.php

Doctrine Mapping Information

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 four metadata formats: YAML, XML, PHP and annotations.

Best Practice

Best Practice

Use annotations to define the mapping information of the Doctrine entities.

Annotations are by far the most convenient and agile way of setting up and looking for mapping information:

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namespace App\Entity;

use Doctrine\ORM\Mapping as ORM;
use Doctrine\Common\Collections\ArrayCollection;

/**
 * @ORM\Entity
 */
class Post
{
    const NUM_ITEMS = 10;

    /**
     * @ORM\Id
     * @ORM\GeneratedValue
     * @ORM\Column(type="integer")
     */
    private $id;

    /**
     * @ORM\Column(type="string")
     */
    private $title;

    /**
     * @ORM\Column(type="string")
     */
    private $slug;

    /**
     * @ORM\Column(type="text")
     */
    private $content;

    /**
     * @ORM\Column(type="string")
     */
    private $authorEmail;

    /**
     * @ORM\Column(type="datetime")
     */
    private $publishedAt;

    /**
     * @ORM\OneToMany(
     *      targetEntity="Comment",
     *      mappedBy="post",
     *      orphanRemoval=true
     * )
     * @ORM\OrderBy({"publishedAt"="ASC"})
     */
    private $comments;

    public function __construct()
    {
        $this->publishedAt = new \DateTime();
        $this->comments = new ArrayCollection();
    }

    // getters and setters ...
}

All formats have the same performance, so this is once again ultimately a matter of taste.

Data Fixtures

As fixtures support is not enabled by default in Symfony, you should execute the following command to install the Doctrine fixtures bundle:

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$ composer require "doctrine/doctrine-fixtures-bundle"

Then, this bundle is enabled automatically, but only for the dev and test environments:

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// config/bundles.php

return [
    // ...
    Doctrine\Bundle\FixturesBundle\DoctrineFixturesBundle::class => ['dev' => true, 'test' => true],
];

We recommend creating just one fixture class for simplicity, though you're welcome to have more if that class gets quite large.

Assuming you have at least one fixtures class and that the database access is configured properly, you can load your fixtures by executing the following command:

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$ php bin/console doctrine:fixtures:load

Careful, database will be purged. Do you want to continue Y/N ? Y
  > purging database
  > loading App\DataFixtures\ORM\LoadFixtures

Coding Standards

The Symfony source code follows the PSR-1 and PSR-2 coding standards that were defined by the PHP community. You can learn more about the Symfony Coding standards and even use the PHP-CS-Fixer, which is a command-line utility that can fix the coding standards of an entire codebase in a matter of seconds.


Next: Controllers

This work, including the code samples, is licensed under a Creative Commons BY-SA 3.0 license.