title: Doctrine ORM order by annotations object fields
body: <p>So its simple like this : I have the following code in some Entity</p>
  
  <pre><code>     /**
       * @var ServiceOffer
       *
       * @ORM\OneToMany(targetEntity="ServiceOffer", mappedBy="serviceProvider")
       * @ORM\OrderBy({"service" = "desc"})
       */
      private $offers;
  </code></pre>
  
  <p>What i need is to do something like this</p>
  
  <pre><code>     /**
       * @var ServiceOffer
       *
       * @ORM\OneToMany(targetEntity="ServiceOffer", mappedBy="serviceProvider")
       * @ORM\OrderBy({"service.points" = "desc"})
       */
      private $offers;
  </code></pre>
  
  <p>which is not working i don't want to do it through some function i wanted straight forward with annotations is there any way to do this ?</p>
  
  <p>this is the points btw:</p>
  
  <pre><code>    /**
       * @var integer
       *
       * @ORM\Column(name="points", type="integer", nullable=true)
       */
      private $points;
  </code></pre>