Creating a table with Arrow FlightΒΆ

Client programs that create tables using Arrow Flight RPC typically follow the below recipe:

  1. Get a FlightWrapper class via TableHandleManager::createFlightWrapper

  2. For calls like Arrow DoPut that take an arrow::Flight::FlightCallOptions, endow that object with Deephaven authentication headers via FlightWrapper::addAuthHeaders

  3. Get a pointer to the arrow::flight::FlightClient from FlightWrapper::flightClient

  4. Then perform the operations as described in Arrow Flight RPC

Consider the following program from cpp-examples/create_table_with_arrow_flight:

#include <iostream>
#include "deephaven/client/highlevel/client.h"
#include "deephaven/client/utility/table_maker.h"

using deephaven::client::highlevel::NumCol;
using deephaven::client::highlevel::Client;
using deephaven::client::highlevel::TableHandle;
using deephaven::client::highlevel::TableHandleManager;
using deephaven::client::utility::flight::statusOrDie;
using deephaven::client::utility::flight::valueOrDie;
using deephaven::client::utility::TableMaker;

// This example shows how to use the Arrow Flight client to make a simple table.
void doit(const TableHandleManager &manager) {
  // 1. Build schema
  arrow::SchemaBuilder schemaBuilder;

  // 2. Add "Symbol" column (type: string) to schema
  auto symbolMetadata = std::make_shared<arrow::KeyValueMetadata>();
  statusOrDie(symbolMetadata->Set("deephaven:type", "java.lang.String"), "KeyValueMetadata::Set");
  auto symbolField = std::make_shared<arrow::Field>("Symbol",
      std::make_shared<arrow::StringType>(), true, std::move(symbolMetadata));
  statusOrDie(schemaBuilder.AddField(symbolField), "SchemaBuilder::AddField");

  // 3. Add "Price" column (type: double) to schema
  auto priceMetadata = std::make_shared<arrow::KeyValueMetadata>();
  statusOrDie(priceMetadata->Set("deephaven:type", "double"), "KeyValueMetadata::Set");
  auto priceField = std::make_shared<arrow::Field>("Price",
      std::make_shared<arrow::StringType>(), true, std::move(priceMetadata));
  statusOrDie(schemaBuilder.AddField(priceField), "SchemaBuilder::AddField");

  // 4. Schema is done
  auto schema = valueOrDie(schemaBuilder.Finish(), "Failed to create schema");

  // 5. Prepare symbol and price data
  std::vector<std::string> symbols{"FB", "AAPL", "NFLX", "GOOG"};
  std::vector<double> prices{101.1, 102.2, 103.3, 104.4};
  auto numRows = static_cast<int64_t>(symbols.size());
  if (numRows != prices.size()) {
    throw std::runtime_error("sizes don't match");
  }

  // 6. Move data to Arrow column builders
  arrow::StringBuilder symbolBuilder;
  arrow::DoubleBuilder priceBuilder;
  symbolBuilder.AppendValues(symbols);
  priceBuilder.AppendValues(prices);

  // 7. Get Arrow columns from builders
  std::vector<std::shared_ptr<arrow::Array>> columns = {
      valueOrDie(symbolBuilder.Finish(), "symbolBuilder.Finish()"),
      valueOrDie(priceBuilder.Finish(), "priceBuilder.Finish()")
  };

  // 8. Get a Deephaven "FlightWrapper" object to access Arrow Flight
  auto wrapper = manager.createFlightWrapper();

  // 9. Allocate a TableHandle and get its corresponding Arrow flight descriptor
  auto [table, fd] = manager.newTableHandleAndFlightDescriptor();

  // 10. DoPut takes FlightCallOptions, which need to at least contain the Deephaven
  // authentication headers for this session.
  arrow::flight::FlightCallOptions options;
  wrapper.addAuthHeaders(&options);

  // 11. Perform the doPut
  std::unique_ptr<arrow::flight::FlightStreamWriter> fsw;
  std::unique_ptr<arrow::flight::FlightMetadataReader> fmr;
  statusOrDie(wrapper.flightClient()->DoPut(options, fd, schema, &fsw, &fmr), "DoPut failed");

  // 12. Make a RecordBatch containing both the schema and the data
  auto batch = arrow::RecordBatch::Make(schema, numRows, std::move(columns));
  statusOrDie(fsw->WriteRecordBatch(*batch), "WriteRecordBatch failed");
  statusOrDie(fsw->DoneWriting(), "DoneWriting failed");

  // 13. Read back a metadata message (ignored), then close the Writer
  std::shared_ptr<arrow::Buffer> buf;
  statusOrDie(fmr->ReadMetadata(&buf), "ReadMetadata failed");
  statusOrDie(fsw->Close(), "Close failed");

  // 14. Use Deephaven high level operations to fetch the table and print it
  std::cout << "table is:\n" << table.stream(true) << std::endl;
}

int main() {
  const char *server = "localhost:10000";
  auto client = Client::connect(server);
  auto manager = client.getManager();

  try {
    doit(manager);
  } catch (const std::runtime_error &e) {
    std::cerr << "Caught exception: " << e.what() << '\n';
  }
}