title: Implement favorites documents in elasticsearch
body: <p>My data model contains two objects - User and Product (stored in mongodb). I have already built a faceted product search using elasticsearch. Now I'm struggling with implementation of "favorite products" - user can mark some products as <em>his</em> favorite and then when searching they should be at the top of the list. The question is - how to model this favorite products marking to make search aware of it and to be able to perform correct sort operation?</p>