title: Loopback filter using related model field
body: <p>Imagine we have two tables, <code>session</code> and <code>movie</code> in postgresql. The table <code>session</code> has a foreignkey to <code>movie</code>. How can i define a relation in <code>movie</code> so that i can ask for movies with filters on <code>session</code>. This table, for example, has a column <code>created</code> and i want to ask for results that has sessions after today with a custom method in Movies.js. </p>