title: Laravel pluck fields from relations
body: <p>I have a Seller object which has a related User. I need to fill a select from LaravelCollective so I need to make something like this:</p>
  
  <pre><code>{!! Form::selectGroup('seller_id', 'Seller', Seller::with('user')-&gt;pluck('user.first_name', 'id')-&gt;toArray(), null) !!}
  </code></pre>
  
  <p>The problem is that I cannot take fields from relationships (user.first_name). </p>
  
  <p>How can I do it?</p>
  
  <p><strong>UPDATE</strong></p>
  
  <p>I want to avoid doing this...</p>
  
  <pre><code>&lt;?php 
      $sellers = [];
  
      Seller::with('user')-&gt;get()-&gt;each(function ($seller) use (&amp;$sellers) {
          $sellers[$seller-&gt;id] = $seller-&gt;user-&gt;first_name;
      });
  ?&gt;
  </code></pre>