title: How do I reference a field value when updating records using Waterline ORM
body: <p>I'm trying to store a hierarchical structure using the Nested Set Model technique. I'm using Waterline ORM for node to query and update my database. How would I model the following query using Waterline?</p>
  
  <p>UPDATE MyTable SET counter=counter+2 WHERE id > 4 AND id &lt; 17;</p>
  
  <p>I'm aware of MyTable.update(...) but I'm not sure how to reference an existing column value in the query.</p>