title: How to add a grouping header when render json:?
body: <p>In the controller:</p>
  
  <pre><code>if @topic.save
    render json: @topic, status: :updated, location: @topic
  else
    render json: @topic.errors, status: :unprocessable_entity
  end
  </code></pre>
  
  <p>Where there is an error, the json response is like:</p>
  
  <pre><code>{"topic_id":["has already been taken"]}
  </code></pre>
  
  <p>How can I add a grouping prefix to the error(s) json response, such that it's easier to be parsed on the client (RestKit) path mapping? e.g.:</p>
  
  <pre><code>{"errors":[{"topic_id":["has already been taken"]}]}
  </code></pre>