/**
  * Retrieving all fields under documents
  * @param $document
  * @return array
  */
 public static function getFields($document)
 {
     $field_mapper = new DocumentFieldValueDBMapper();
     $fields = $field_mapper->getFieldsByDocumentIdAndDocumentTimestamp($document->getId(), $document->getTimestamp());
     $field_array = [];
     foreach ($fields as $field) {
         array_push($field_array, $field->toArray());
     }
     return $field_array;
 }