title: Doctrine2 association mapping with conditions
body: <p>is it possible to have association mapping with conditions in Doctrine 2.4? I have entities Article and Comment. Comments needs to be approved by admin. Approval status of comment is stored in boolean field "approved. </p>
  
  <p>Now I have @OneToMany association mapping to comments in entity Article. It maps all the comments. But I would like to map only approved comments. </p>
  
  <p>Something like</p>
  
  <pre><code>@ORM\OneToMany(targetEntity="Comment", where="approved=true", mappedBy="article")
  </code></pre>
  
  <p>would be very helpful. Unfortunately AFAIK there is no such thing as where condition in mapping, so I tried to solve my problem with inheritance - I created two subclasses of class Comment. Now I have ApprovedComment and NotApprovedComment and SINGLE_TABLE inheritance mapping. </p>
  
  <pre><code> @ORM\InheritanceType("SINGLE_TABLE")
   @ORM\DiscriminatorColumn(name="approved", type="integer")
   @ORM\DiscriminatorMap({1 = "ApprovedComment", 0 = "NotApprovedComment"})
  </code></pre>
  
  <p>Problem is, since "approved" column is discriminator, I cannot use it as field in entity Comment anymore. </p>