code: def _load_mapping(self, mapping):
          
          mapping["oid_as_pk"] = bool(mapping.get("fields", {}).get("Id"))
          job_id, local_ids_for_batch = self._create_job(mapping)
          result = self._wait_for_job(job_id)
          # We store inserted ids even if some batches failed
          self._store_inserted_ids(mapping, job_id, local_ids_for_batch)
          return result
docs: Load data for a single step.