/**
  * Implements SearchEngineAbstract::indexDocument().
  *
  * @param CollectionAbstract $collection
  * @param IndexDocument $document
  */
 public function indexDocument(CollectionAbstract $collection, IndexDocument $document)
 {
     $index_doc = array();
     if (null !== ($boost = $document->getBoost())) {
         $index_doc['_boost'] = $boost;
     }
     foreach ($document as $field_id => $normalized_value) {
         $name = $document->getFieldName($field_id);
         $index_doc[$name] = $normalized_value;
     }
     $native_doc = new Elastica_Document(null, $index_doc);
     $native_doc->setIndex($this->_activeIndex);
     $native_doc->setType($collection->getType());
     $this->_documents[] = $native_doc;
 }