/**
  * Creates a filter protobuffer message
  * @param  \App_ListFilter          $filterList
  * @return DrSlump\ProtoBuf\Message type of $_filterClass, defined above.
  */
 protected function _createFilter(\App_ListFilter_CollectionAbstract $filterList)
 {
     $criterias = $filterList->getFilters();
     $mongoFilter = array();
     foreach ($criterias as $filter) {
         if ($mappedFilter = $this->_mapFilterToMongoFilter($filter)) {
             $mongoFilter = array_merge_recursive($mongoFilter, $mappedFilter);
         }
     }
     return $mongoFilter;
 }
 protected function _constructFieldName()
 {
     return 'OR' . parent::_constructFieldName();
 }