title: Call to undefined method Illuminate\Database\Query\Builder::only()
body: <p>I'm using Laravel 4.2 framework php. I want to retrieve the id where the username will be equal to what I want to find. I want to find username's id basically. I'm use only method, to retrieve 'id' but didn't work. It tells me method not working. Perhaps I has different version of :aravel version.</p>
  
  <pre><code>$user_id = User::where('username','=',$username)-&gt;only('id');
  </code></pre>