def document_changes(document)
      (document.changed + document._children.select{|child| child.changed? }.map { |child|
        "#{child.metadata_name.to_s}{#{child.changed.join(", ")}}"
      }).join(", ")
    end
def document_changes(document)
      (document.changed + document._children.select{|child| child.changed? }.map { |child|
        "#{child.metadata_name.to_s}{#{child.changed.join(", ")}}"
      }).join(", ")
    end
List changed fields of model
 @param document [Mongoid::Document]
 @return [String] field, embedded{field}