title: Add calculated value to OData result
body: <p>I'm trying to add some info to the data result whether the user has read or write access to the entity.</p>
  
  <p>Lets assume I have this entity:</p>
  
  <pre><code>public class Foo
  {
     public int Id { get; set; }
     public string Name { get; set; }
     public virtual ICollection&lt;Access&gt; AccessRights { get; set; }
  }
  </code></pre>
  
  <p>Where <code>AccessRights</code> holds the user id and if they have read/write access.</p>
  
  <p>Currently I just <code>$expand</code> AccessRights and calculate if the user has read/write access in the frontend. However I'd like this calculated property to be added to the result.</p>
  
  <p>Example json result:</p>
  
  <pre><code>{
     id: 1,
     name: "foo",
     hasReadAccess: true,
     hasWriteAccess: true
  }
  </code></pre>
  
  <p>Is it possible to do this? Keep in mind that <code>HasRead/WriteAccess</code> doesn't exist on the model nor should it.</p>