title: Sailsjs what attribute does findOrCreate use to find if a record exists?
body: <p>I'm using sailsjs with mysql, and using it to save data from a shopify webhook when an order is placed. It returns a json object, and one of the properties is a customer object, which I'm saving in a different table related back to the main orders table. I'm using findOrCreate on the customer model so I don't have duplicate customers. </p>
  
  <p>Can waterline use a specific attribute to determine if a record is already present? The customer object (from shopify) has an id, but the docs doesn't make it clear if this is going to be the same for a given customer across different orders. Also, if a customer sets a different payment method, billing address, etc would waterline create a new record for it? </p>
  
  <p>To sum up, I need waterline to use the customer_email property to determine if a record exists or not. Is this possible? Sorry for the rambling; I'm thinking through this as I type. </p>