def _load_mapping(self, mapping):
        """Load data for a single step."""
        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
Load data for a single step.