wjones127 commented on code in PR #12775: URL: https://github.com/apache/arrow/pull/12775#discussion_r895489955
########## cpp/examples/arrow/rapidjson_row_converter.cc: ########## @@ -0,0 +1,590 @@ +// Licensed to the Apache Software Foundation (ASF) under one +// or more contributor license agreements. See the NOTICE file +// distributed with this work for additional information +// regarding copyright ownership. The ASF licenses this file +// to you under the Apache License, Version 2.0 (the +// "License"); you may not use this file except in compliance +// with the License. You may obtain a copy of the License at +// +// http://www.apache.org/licenses/LICENSE-2.0 +// +// Unless required by applicable law or agreed to in writing, +// software distributed under the License is distributed on an +// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY +// KIND, either express or implied. See the License for the +// specific language governing permissions and limitations +// under the License. + +#include <arrow/api.h> +#include <arrow/result.h> +#include <arrow/table_builder.h> +#include <arrow/type_traits.h> +#include <arrow/util/iterator.h> +#include <arrow/util/logging.h> +#include <arrow/visit_array_inline.h> + +#include <rapidjson/document.h> +#include <rapidjson/stringbuffer.h> +#include <rapidjson/writer.h> + +#include <cassert> +#include <iostream> +#include <vector> + +// Transforming dynamic row data into Arrow data +// When building connectors to other data systems, it's common to receive data in +// row-based structures. While the row_wise_conversion_example.cc shows how to +// handle this conversion for fixed schemas, this example demonstrates how to +// writer converters for arbitrary schemas. +// +// As an example, this conversion is between Arrow and rapidjson::Documents. +// +// We use the following helpers and patterns here: +// * arrow::ToRowConverter and arrow::FromRowConverter, which provide additional +// conversion methods given a basic converter +// * arrow::VisitArrayInline and arrow::VisitTypeInline for implementing a visitor +// pattern with Arrow to handle different array types +// * arrow::enable_if_primitive_ctype to create a template method that handles +// * conversion for Arrow types that have corresponding C types (bool, integer, +// float). + +rapidjson::Value kNullJsonSingleton = rapidjson::Value(); + +/// \brief Builder that holds state for a single conversion. +/// +/// Implements Visit() methods for each type of Arrow Array that set the values +/// of the corresponding fields in each row. +class RowBatchBuilder { + public: + explicit RowBatchBuilder(int64_t num_rows) : field_(nullptr) { + // Reserve all of the space required up-front to avoid unnecessary resizing + rows_.reserve(num_rows); + + for (int64_t i = 0; i < num_rows; ++i) { + rows_.push_back(rapidjson::Document()); + rows_[i].SetObject(); + } + } + + /// \brief Set which field to convert. + void SetField(std::shared_ptr<arrow::Field> field) { field_ = std::move(field); } + + /// \brief Retrieve converted rows from builder. + std::vector<rapidjson::Document> Rows() && { return std::move(rows_); } + + // Default implementation + arrow::Status Visit(const arrow::Array& array) { + return arrow::Status::NotImplemented( + "Can not convert to json document for array of type ", array.type()->ToString()); + } + + // Handles booleans, integers, floats + template <typename ArrayType, typename DataClass = typename ArrayType::TypeClass> + arrow::enable_if_primitive_ctype<DataClass, arrow::Status> Visit( + const ArrayType& array) { + for (int64_t i = 0; i < array.length(); ++i) { + if (!array.IsNull(i)) { + rapidjson::Value str_key(field_->name().c_str(), rows_[i].GetAllocator()); + rows_[i].AddMember(str_key, array.Value(i), rows_[i].GetAllocator()); + } + } + return arrow::Status::OK(); + } + + arrow::Status Visit(const arrow::StringArray& array) { + for (int64_t i = 0; i < array.length(); ++i) { + if (!array.IsNull(i)) { + rapidjson::Value str_key(field_->name().c_str(), rows_[i].GetAllocator()); + // StringArray.Value returns a string view + auto value_view = array.Value(i); + rapidjson::Value value; + value.SetString(value_view.data(), + static_cast<rapidjson::SizeType>(value_view.size()), + rows_[i].GetAllocator()); + rows_[i].AddMember(str_key, value, rows_[i].GetAllocator()); + } + } + return arrow::Status::OK(); + } + + arrow::Status Visit(const arrow::StructArray& array) { + const arrow::StructType* type = array.struct_type(); + + RowBatchBuilder child_builder(rows_.size()); + for (int i = 0; i < type->num_fields(); ++i) { + std::shared_ptr<arrow::Field> child_field = type->field(i); + child_builder.SetField(std::move(child_field)); + ARROW_RETURN_NOT_OK(arrow::VisitArrayInline(*array.field(i).get(), &child_builder)); + } + std::vector<rapidjson::Document> rows = std::move(child_builder).Rows(); + + for (int64_t i = 0; i < array.length(); ++i) { + if (!array.IsNull(i)) { + rapidjson::Value str_key(field_->name().c_str(), rows_[i].GetAllocator()); + // Must copy value to new allocator + rapidjson::Value row_val; + row_val.CopyFrom(rows[i], rows_[i].GetAllocator()); + rows_[i].AddMember(str_key, row_val, rows_[i].GetAllocator()); + } + } + return arrow::Status::OK(); + } + + arrow::Status Visit(const arrow::ListArray& array) { + // First create rows from values + std::shared_ptr<arrow::Array> values = array.values(); + RowBatchBuilder child_builder(values->length()); + std::shared_ptr<arrow::Field> value_field = array.list_type()->value_field(); + std::string value_field_name = value_field->name(); + child_builder.SetField(value_field); + ARROW_RETURN_NOT_OK(arrow::VisitArrayInline(*values.get(), &child_builder)); + + std::vector<rapidjson::Document> rows = std::move(child_builder).Rows(); + + int64_t values_i = 0; + for (int64_t i = 0; i < array.length(); ++i) { + rapidjson::Document::AllocatorType& allocator = rows_[i].GetAllocator(); + auto array_len = array.value_length(i); + + rapidjson::Value value; + value.SetArray(); + value.Reserve(array_len, allocator); + + for (int64_t j = 0; j < array_len; ++j) { + rapidjson::Value row_val; + // Must copy value to new allocator + row_val.CopyFrom(rows[values_i][value_field_name.c_str()], allocator); + value.PushBack(row_val, allocator); + ++values_i; + } + + rapidjson::Value str_key(field_->name().c_str(), allocator); + rows_[i].AddMember(str_key, value, allocator); + } + + return arrow::Status::OK(); + } + + private: + std::shared_ptr<arrow::Field> field_; + std::vector<rapidjson::Document> rows_; +}; // RowBatchBuilder + +class ArrowToDocumentConverter : public arrow::ToRowConverter<rapidjson::Document> { + public: + arrow::Result<std::vector<rapidjson::Document>> ConvertToVector( + std::shared_ptr<arrow::RecordBatch> batch) override { + RowBatchBuilder builder{batch->num_rows()}; + + for (int i = 0; i < batch->num_columns(); ++i) { + builder.SetField(std::move(batch->schema()->field(i))); + ARROW_RETURN_NOT_OK(arrow::VisitArrayInline(*batch->column(i).get(), &builder)); + } + + return std::move(builder).Rows(); + } +}; // ArrowToDocumentConverter + +/// \brief Iterator over rows values of a document for a given field +/// +/// path and array_levels are used to address each field in a JSON document. As +/// an example, consider this JSON document: +/// { +/// "x": 3, // path: ["x"], array_levels: 0 +/// "files": [ // path: ["files"], array_levels: 0 +/// { // path: ["files"], array_levels: 1 +/// "path": "my_str", // path: ["files", "path"], array_levels: 1 +/// "sizes": [ // path: ["files", "size"], array_levels: 1 +/// 20, // path: ["files", "size"], array_levels: 2 +/// 22 +/// ] +/// } +/// ] +/// }, +class DocValuesIterator { + public: + /// \param rows vector of rows + /// \param path field names to enter + /// \param array_levels number of arrays to enter + DocValuesIterator(const std::vector<rapidjson::Document>& rows, + std::vector<std::string> path, int64_t array_levels) + : rows(rows), path(std::move(path)), array_levels(array_levels) {} + + const rapidjson::Value* NextArrayOrRow(const rapidjson::Value* value, size_t* path_i, + int64_t* arr_i) { + while (array_stack.size() > 0) { + ArrayPosition& pos = array_stack.back(); + // Try to get next position in Array + if (pos.index + 1 < pos.array_node->Size()) { + ++pos.index; + value = &(*pos.array_node)[pos.index]; + *path_i = pos.path_index; + *arr_i = array_stack.size(); + return value; + } else { + array_stack.pop_back(); + } + } + ++row_i; + if (row_i < rows.size()) { + value = static_cast<const rapidjson::Value*>(&rows[row_i]); + } else { + value = nullptr; + } + *path_i = 0; + *arr_i = 0; + return value; + } + + arrow::Result<const rapidjson::Value*> Next() { + const rapidjson::Value* value = nullptr; + size_t path_i; + int64_t arr_i; + // Can either start at document or at last array level + if (array_stack.size() > 0) { + auto pos = array_stack.back(); + value = pos.array_node; + path_i = pos.path_index; + arr_i = array_stack.size() - 1; + } + + value = NextArrayOrRow(value, &path_i, &arr_i); + + // Traverse to desired level (with possible backtracking as needed) + while (path_i < path.size() || arr_i < array_levels) { + if (value == nullptr) { + return value; + } else if (value->IsArray() && value->Size() > 0) { + ArrayPosition pos; + pos.array_node = value; + pos.path_index = path_i; + pos.index = 0; + array_stack.push_back(pos); + + value = &(*value)[0]; + ++arr_i; + } else if (value->IsArray()) { + // Empty array means we need to backtrack and go to next array or row + value = NextArrayOrRow(value, &path_i, &arr_i); + } else if (value->HasMember(path[path_i].c_str())) { + value = &(*value)[path[path_i].c_str()]; + ++path_i; + } else { + return &kNullJsonSingleton; + } + } + + // Return value + return value; + } + + protected: + const std::vector<rapidjson::Document>& rows; + std::vector<std::string> path; + int64_t array_levels; + size_t row_i = -1; // index of current row + + // Info about array position for one array level in array stack + struct ArrayPosition { + const rapidjson::Value* array_node; + int64_t path_index; + rapidjson::SizeType index; + }; + std::vector<ArrayPosition> array_stack; +}; + +class JsonValueConverter { + public: + explicit JsonValueConverter(const std::vector<rapidjson::Document>& rows) + : rows_(rows), array_levels_(0) {} + + JsonValueConverter(const std::vector<rapidjson::Document>& rows, + const std::vector<std::string>& root_path, int64_t array_levels) + : rows_(rows), root_path_(root_path), array_levels_(array_levels) {} + + /// \brief For field passed in, append corresponding values to builder + arrow::Status Convert(const arrow::Field& field, arrow::ArrayBuilder* builder) { + return Convert(field, field.name(), builder); + } + + /// \brief For field passed in, append corresponding values to builder + arrow::Status Convert(const arrow::Field& field, const std::string& field_name, + arrow::ArrayBuilder* builder) { + field_name_ = field_name; + builder_ = builder; + ARROW_RETURN_NOT_OK(arrow::VisitTypeInline(*field.type().get(), this)); + return arrow::Status::OK(); + } + + // Default implementation + arrow::Status Visit(const arrow::DataType& type) { + return arrow::Status::NotImplemented( + "Can not convert to json document for array of type ", type.ToString()); Review Comment: Yup, thanks! -- This is an automated message from the Apache Git Service. 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