public function getSortFieldName(SortClause $sortClause, $contentTypeIdentifier, $fieldDefinitionIdentifier, $name = null)
{
$fieldMap = $this->getSearchableFieldMap();
// First check if field exists in type, there is nothing to do if it doesn't
if (!isset($fieldMap[$contentTypeIdentifier][$fieldDefinitionIdentifier])) {
return null;
}
$fieldName = array_keys($this->getIndexFieldName($sortClause, $contentTypeIdentifier, $fieldDefinitionIdentifier, $fieldMap[$contentTypeIdentifier][$fieldDefinitionIdentifier]['field_type_identifier'], $name, true));
return reset($fieldName);
}