title: Grape::Entities, how to expose property only for writing
body: <p>how can i expose revision property of VehicleDetails that will not appear on <strong>GET</strong> request, but will be obligatory on <strong>PATCH/POST</strong> (<strong>only writing operations</strong>)?</p>
  
  <pre><code>class VehicleDetails &lt; Grape::Entity
    expose :id
    expose :name
    expose :type
    expose :revision
  end
  </code></pre>