title: How to serialize only the ID of a child with Jackson
body: <p>Is there a built-in way to only serialize the id of a child when using Jackson (fasterxml.jackson 2.1.1)? We want to send an <code>Order</code> via REST which has a <code>Person</code> reference. The person object however is quite complex and we could refresh it on the server side, so all we need is the primary key.</p>
  
  <p>Or do I need a custom serializer for this? Or do I need to <code>@JsonIgnore</code> all other properties? Would that prevent the <code>Person</code> data from being sent back when requesting an <code>Order</code> object? I'm not sure yet if I'll need that but I'd like to have control over it if possible...</p>