symfony
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+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 everything inside the ``AppBundle``.
+Inside here, you can create whatever directories you want to organize things:
+
+.. code-block:: text
+
+    symfoy2-project/
+    ├─ app/
+    ├─ src/
+    │  └─ AppBundle/
+    │     └─ Utils/
+    │        └─ MyClass.php
+    ├─ vendor/
+    └─ web/
+
+Storing Classes Outside of the Bundle?
+--------------------------------------
+
+But there's no technical reason for putting business logic inside of a bundle.
+If you like, you can create your own namespace inside the ``src/`` directory
+and put things there:
+
+.. code-block:: text
+
+    symfoy2-project/
+    ├─ app/
+    ├─ src/
+    │  ├─ Acme/
+    │  │   └─ Utils/
+    │  │      └─ MyClass.php
+    │  └─ AppBundle/
+    ├─ vendor/
+    └─ web/
+
+.. tip::
+
+    The recommended approach of using the ``AppBundle`` directory is for
+    simplicity. If you're advanced enough to know what needs to live in
+    a bundle and what can live outside of one, then feel free to do that.
+
+Services: Naming and Format
+---------------------------
+
+The blog application needs a utility that can transform a post title (e.g.
+"Hello World") into a slug (e.g. "hello-world"). The slug will be used as
+part of the post URL.
+
+Let's, create a new ``Slugger`` class inside ``src/AppBundle/Utils/`` and
+add the following ``slugify()`` method:
+
+.. code-block:: php
+
+    // src/AppBundle/Utils/Slugger.php
+    namespace AppBundle\Utils;
+
+    class Slugger
+    {
+        public function slugify($string)
+        {
+            return preg_replace(
+                '/[^a-z0-9]/', '-', strtolower(trim(strip_tags($string)))
+            );
+        }
+    }
+
+Next, define a new service for that class.
+
+.. code-block:: yaml
+
+    # app/config/services.yml
+    services:
+        # keep your service names short
+        slugger:
+            class: AppBundle\Utils\Slugger
+
+Traditionally, the naming convention for a service involved following the
+class name and location to avoid name collisions. Thus, the service
+*would have been* called ``app.utils.slugger``. But by using short service names,
+your code will be easier to read and use.
+
+.. best-practice::
+
+    The name of your application's services should be as short as possible,
+    ideally just one simple word.
+
+Now you can use the custom slugger in any controller class, such as the
+``AdminController``:
+
+.. code-block:: php
+
+    public function createAction(Request $request)
+    {
+        // ...
+
+        if ($form->isSubmitted() && $form->isValid()) {
+            $slug = $this->get('slugger')->slugify($post->getTitle()));
+            $post->setSlug($slug);
+
+            // ...
+        }
+    }
+
+Service Format: YAML
+--------------------
+
+In the previous section, YAML was used to define the service.
+
+.. 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.
+
+Service: No Class Parameter
+---------------------------
+
+You may have noticed that the previous service definition doesn't configure
+the class namespace as a parameter:
+
+.. code-block:: yaml
+
+    # app/config/services.yml
+
+    # service definition with class namespace as parameter
+    parameters:
+        slugger.class: AppBundle\Utils\Slugger
+
+    services:
+        slugger:
+            class: "%slugger.class%"
+
+This practice is cumbersome and completely unnecessary for your own services:
+
+.. best-practice::
+
+    Don't define parameters for the classes of your services.
+
+This practice was wrongly adopted from third-party bundles. When Symfony
+introduced its service container, some developers used this technique to easily
+allow overriding services. However, overriding a service by just changing its
+class name is a very rare use case because, frequently, the new service has
+different constructor arguments.
+
+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 ``AppBundle``
+
+The three entities defined by our sample blog application are a good example:
+
+.. code-block:: text
+
+    symfony2-project/
+    ├─ ...
+    └─ src/
+       └─ AppBundle/
+          └─ Entity/
+             ├─ Comment.php
+             ├─ Post.php
+             └─ User.php
+
+.. tip::
+
+    If you're more advanced, you can of course store them under your own
+    namespace in ``src/``.
+
+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::
+
+    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:
+
+.. code-block:: php
+
+    namespace AppBundle\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:
+
+.. code-block:: bash
+
+    $ composer require "doctrine/doctrine-fixtures-bundle"
+
+Then, enable the bundle in ``AppKernel.php``, but only for the ``dev`` and
+``test`` environments:
+
+.. code-block:: php
+
+    use Symfony\Component\HttpKernel\Kernel;
+
+    class AppKernel extends Kernel
+    {
+        public function registerBundles()
+        {
+            $bundles = array(
+                // ...
+            );
+
+            if (in_array($this->getEnvironment(), array('dev', 'test'))) {
+                // ...
+                $bundles[] = new Doctrine\Bundle\FixturesBundle\DoctrineFixturesBundle(),
+            }
+
+            return $bundles;
+        }
+
+        // ...
+    }
+
+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:
+
+.. code-block:: bash
+
+    $ php app/console doctrine:fixtures:load
+
+    Careful, database will be purged. Do you want to continue Y/N ? Y
+      > purging database
+      > loading AppBundle\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 Code 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.
+
+.. _`full definition`: http://en.wikipedia.org/wiki/Business_logic
+.. _`Toran Proxy`: https://toranproxy.com/
+.. _`Composer`: https://getcomposer.org/
+.. _`MVC architecture`: http://en.wikipedia.org/wiki/Model%E2%80%93view%E2%80%93controller
+.. _`Doctrine project`: http://www.doctrine-project.org/
+.. _`fixture class`: http://symfony.com/doc/master/bundles/DoctrineFixturesBundle/index.html#writing-simple-fixtures
+.. _`PSR-1`: http://www.php-fig.org/psr/psr-1/
+.. _`PSR-2`: http://www.php-fig.org/psr/psr-2/
+.. _`the Symfony Code Standards`: http://symfony.com/doc/current/contributing/code/standards.html
+.. _`PHP-CS-Fixer`: https://github.com/fabpot/PHP-CS-Fixer