public function getIndexFieldType($field)
 {
     if (!self::$indexFieldTypes) {
         self::$indexFieldTypes = array('category_id' => IIndexable::FIELD_TYPE_STRING, 'kuser_id' => IIndexable::FIELD_TYPE_STRING, 'category_full_ids' => IIndexable::FIELD_TYPE_STRING, 'permission_names' => IIndexable::FIELD_TYPE_STRING, 'puser_id' => IIndexable::FIELD_TYPE_STRING, 'screen_name' => IIndexable::FIELD_TYPE_STRING, 'category_kuser_status' => IIndexable::FIELD_TYPE_STRING, 'partner_id' => IIndexable::FIELD_TYPE_STRING, 'update_method' => IIndexable::FIELD_TYPE_STRING, 'created_at' => IIndexable::FIELD_TYPE_DATETIME, 'updated_at' => IIndexable::FIELD_TYPE_DATETIME);
     }
     if (isset(self::$indexFieldTypes[$field])) {
         return self::$indexFieldTypes[$field];
     }
     return null;
 }