title: How to query a field by name on mongoid?
body: <p>How can I get the same query's result :</p>
  
  <pre><code>Test.where(name: "Depeche Mode").first.last_connection_date
  </code></pre>
  
  <p>Changing <code>last_connection_date</code> by a String</p>
  
  <pre><code>@desired_field = "last_connection_date"
  Test.where(name: "Depeche Mode").first.(@desired_field)
  </code></pre>