title: Sort a doctrine's @OneToMany ArrayCollection
body: <p>My question is close to <a href="https://stackoverflow.com/questions/16705425/usort-a-doctrine-common-collections-arraycollection">this one</a>, but does not exactly fit with mine.</p>
  
  <p>I've this column in an entity:</p>
  
  <pre><code>/**
   * @var ArrayCollection[SubjectTag]
   *
   * @ORM\OneToMany(targetEntity="SubjectTag", mappedBy="subject")
   * @Assert\Count(max = 10, maxMessage = "You can't create more than 10 tags.")
   * @Assert\Valid()
   */
  protected $subjectTags;
  </code></pre>
  
  <p>I want to dynamically order my tags by a position, defined in <code>SubjectTag.position</code>. </p>