title: Eloquent firstOrNew causes duplicate entry error
body: <p>I'm trying to find an item and update it if it exists, or to create a new one if it does not exist. However, for some reason it seems to be trying to create a new object instead of updating in the event that that already exists in the database.</p>
  
  <pre><code>    $object = ObjectItem::firstOrNew(array('object_item_id'=&gt;$userEditedObject['object_item_id'], 'object_id'=&gt;$object_id));
  
      $object-&gt;setFields($userEditedObject);
  
      if($object-&gt;save()){
          return TRUE;
      } else {
          return FALSE;
      }
  </code></pre>
  
  <p>That code appears to be producing the error </p>
  
  <p><code>"SQLSTATE[23000]: Integrity constraint violation: 1062 Duplicate entry '113' for key 'PRIMARY'</code></p>
  
  <p>This is strange, because I have used this before and it worked okay -- it just seems to be in this particular case.</p>