docstr: Register relationship between data subject and it's member.
docstr_tok: ["Register","relationship","between","data","subject","and","it","'s","member","."]
code: def add(
      self, context: AuthedServiceContext, parent: str, child: str
  ) -> Union[SyftSuccess, SyftError]:
      """Register relationship between data subject and it's member."""
      relation = DataSubjectMemberRelationship(
          parent=parent, child=child
      )
      result = self.stash.set(
          context.credentials, relation, ignore_duplicates=True
      )
      if result.is_err():
          return SyftError(result.err())
      return SyftSuccess(
          message=f"Relationship added for: {parent} -> {child}"
      )
  
imports: from typing import List
  from typing import Optional
  from typing import Union
  from result import Result
  from ...node.credentials import SyftVerifyKey
  from ...serde.serializable import serializable
  from ...store.document_store import BaseUIDStoreStash
  from ...store.document_store import DocumentStore
  from ...store.document_store import PartitionSettings
  from ...store.document_store import QueryKeys
  from ...util.telemetry import instrument
  from ..context import AuthedServiceContext
  from ..response import SyftError
  from ..response import SyftSuccess
  from ..service import AbstractService
  from ..service import SERVICE_TO_TYPES
  from ..service import TYPE_TO_SERVICE
  from .data_subject_member import ChildPartitionKey
  from .data_subject_member import DataSubjectMemberRelationship
  from .data_subject_member import ParentPartitionKey
label_desc: Use image node_id 2 for calling the DataSubjectMemberService obj's underlying member method code with example usage: obj.add(context, parent, child) and returns: SyftSuccess, SyftError