title: Laravel Eloquent - firstOrCreate() on a relationship
body: <p>When I try the <code>firstOrCreate()</code> on a relationship of another model, it does not work:</p>
  
  <pre><code>Client::find($id)-&gt;users()-&gt;firstOrCreate(array('email' =&gt; $email));
  </code></pre>
  
  <p>This returns an error saying </p>
  
  <blockquote>
    <p>Call to undefined method Illuminate\Database\Query\Builder::firstOrCreate()</p>
  </blockquote>
  
  <p>Running this directly on the model <code>User</code> will work though. </p>