issuable_base_service.rb

class IssuableBaseService < BaseService
  private

  def create_assignee_note(issuable)
    SystemNoteService.assignee_change(
      issuable, issuable.project, current_user, issuable.assignee)
  end

  def create_milestone_note(issuable)
    SystemNoteService.milestone_change(
      issuable, issuable.project, current_user, issuable.milestone)
  end

  def create_labels_note(issuable, added_labels, removed_labels)
    SystemNoteService.label_change(
      issuable, issuable.project, current_user, added_labels, removed_labels)
  end
end