title: Return model where the pivot entry exists
body: <p>I'm using BookshelfJS. I have two models <code>users</code> and <code>posts</code>. Obviously, the relationship here is many to many. So I have a pivot table <code>post_user</code>. </p>
  
  <p>Now, given a <code>user_id</code>, I want to find all the <code>posts</code> for that user. So far, I've managed to do this using <code>knex</code>:</p>
  
  <pre><code>knex.select()
      .from('post_user')
      .where('user_id', user_id)
      .then(function (pivots) {
          // Now loop through pivots and return all the posts
          // Using pivot.post_id
          pivots.map(function(pivot) {})
      });
  </code></pre>
  
  <p>Is there a cleaner way of doing this?</p>