title: Return only one attribute in a mongodb query
body: <pre><code>@Query("{'recibido' : null ,'activo' : true}")
  public List&lt;Long&gt; findEmpleadosPrlActivoRecibidoIsNull();
  </code></pre>
  
  <p>I want you to return a list with the "employee_id" attribute of each object and not the whole object.</p>
  
  <p>Can somebody help me.</p>
  
  <p>Thank you.</p>