code: def get_relationship_model(manager, relationship_id):
      
      bundle = get_relationship_bundle(manager, relationship_id)
      return models.BaseRelationshipModel(manager).load(bundle)
docs: :param manager: Context manager to handle transactions
      :type manager: Neo4jDBSessionManager
      :param relationship_id: Internal Neo4j relationship id
      :type relationship_id: int
      :return: Relationship model
      :rtype: models.BaseRelationshipModel