How to easily manage your OneToMany doctrine relationship in a Symfony form

OneToMany-Remove-Example.php

<?php

/*
  This is an example of how to easily manage a OneToMany relationship in a 
  Doctrine Entity with minimal code.
*/


$req = new Req();
$form = $this->createForm('AppBundle\Form\Type\MyType', $req);
$form->handleRequest($request);
if ($form->isValid()) {
  // remove deleted tags (only needed on existing records)
  // no need to create a cloned list before you create the form above, like some examples show.
  if ($req->getId() !== null) {
      /** @var PersistentCollection $original */
      $original = $req->getTags();
      // The snapshot has the original list before modification by the form
      foreach ($original->getSnapshot() as $tag) {
          if (!$req->getTags()->contains($tag)) {
              $em->remove($tag);
          }
      }
  }

  try {
      $em->persist($req);
      $em->flush();
  } catch (\Exception $e) {
    // error
  }
}

Req.php

<?php

/**
 * @ORM\Entity
 */
class Req
{
    /**
     * @var integer
     *
     * @ORM\Column(type="integer")
     * @ORM\Id
     * @ORM\GeneratedValue(strategy="AUTO")
     */
    protected $id;

    /**
     * @var ArrayCollection
     *
     * INVERSE SIDE
     * @ORM\OneToMany(targetEntity="Network", mappedBy="request", cascade={"persist"})
     */
    protected $tags;
  
}

Tag.php

<?php

class Tag
{
    /**
     * @ORM\Id
     * @ORM\Column(type="integer")
     * @ORM\GeneratedValue(strategy="AUTO")
     *
     * @var integer $id
     */
    protected $id;

    /**
     * @var Req
     * 
     * OWNING SIDE
     * @ORM\ManyToOne(targetEntity="Req", inversedBy="tags", cascade={"persist"})
     * @ORM\JoinColumn(onDelete="CASCADE")
     */
    protected $req;
    
}