code: def get_object_id(self, datum):
          
  
          # Role assignment doesn't have identifier so one will be created
          # from the identifier of scope, user and role. This will guaranty the
          # unicity.
          scope_id = ""
          if "project" in datum.scope:
              scope_id = datum.scope["project"]["id"]
          elif "domain" in datum.scope:
              scope_id = datum.scope["domain"]["id"]
  
          assignee_id = ""
          if hasattr(datum, "user"):
              assignee_id = datum.user["id"]
          elif hasattr(datum, "group"):
              assignee_id = datum.group["id"]
  
          return "%s%s%s" % (assignee_id, datum.role["id"], scope_id)
docs: Identifier of the role assignment.