Method latestStringAt

pj_datastore/src/reader.cpp:212–236

}

PJ::Expected<std::optional<std::string>> DataReader::latestStringAt(
    const QueryPoint& point, std::size_t column_index) const {
  auto lock = engine_.lockEngine();
  const TopicStorage* storage = engine_.getTopicStorage(point.topic_id);
  if (storage == nullptr) {
    return PJ::unexpected(fmt::format("Topic {} not found", point.topic_id));
  }
  const std::optional<SampleRow> row = PJ::latestAt(storage->sealedChunks(), point.t, storage->retentionFloor());
  if (!row.has_value()) {
    return std::optional<std::string>{};
  }
  // Guard the column index (chunks before a mid-stream column add have fewer
  // columns), the string-ness of the column (readString is UB on a numeric
  // column), and nulls — then copy the value out WHILE the lock is held, since
  // readString views chunk-internal dictionary memory that must not escape.
  if (column_index >= row->chunk->columns.size()) {
    return std::optional<std::string>{};
  }
  const auto& descriptor = row->chunk->columns[column_index].descriptor;
  if (descriptor == nullptr || descriptor->logical_type != PrimitiveType::kString ||
      row->chunk->isNull(column_index, row->row_index)) {
    return std::optional<std::string>{};
  }
  return std::optional<std::string>{std::string(row->chunk->readString(column_index, row->row_index))};
}

Expected<SeriesReader> DataReader::series(TopicId topic_id, std::size_t column_index) const {
  auto lock = engine_.lockEngine();