/**
  * {@inheritdoc}
  */
 public function addFilter(Collection $collection, $field, $condition = null)
 {
     if (isset($condition['from'])) {
         $collection->getSelect()->where(AbstractCollection::ATTRIBUTE_TABLE_ALIAS_PREFIX . 'qty.qty >= ?', (double) $condition['from']);
     }
     if ($condition['to']) {
         $collection->getSelect()->where(AbstractCollection::ATTRIBUTE_TABLE_ALIAS_PREFIX . 'qty.qty <= ?', (double) $condition['to']);
     }
 }