我有 json 格式的数据，想将其转换为 csv

Question

#include <bsoncxx/builder/stream/document.hpp>
#include <bsoncxx/json.hpp>
#include <mongocxx/client.hpp>
#include <mongocxx/instance.hpp>
#include <fstream>
#include <iostream>
#include <string>

using namespace std;
int main()
{
    ofstream myfile;
    myfile.open("newtest.csv");
    mongocxx::instance instance{};
    mongocxx::uri uri("mongodb://localhost:27017");
    mongocxx::client client(uri);
    mongocxx::database db = client["work"];
    mongocxx::collection coll = db["User"];
    bsoncxx::stdx::optional<bsoncxx::document::value> maybe_result = coll.find_one({});
}

maybe_result 中的 JSON：

{
    "_id": {
        "$oid": "5f2a435186ff70fb16f873ec"
    },
    "first_name": "Gutta",
    "last_name": "sumanth",
    "age": 25.0,
    "employee_status": "active",
    "email": "sumanth@gmail.com"
}

我想将输出更改为 csv 格式。

Answer 1

这是一种方法。在此示例中，bsoncxx::types 比我想解码的要多一些。如果您需要它们，则必须添加它们。这应该足以将您的bson 数据输出为csv。

我已将支持函数放在一个类中以支持流式传输到任何std::ostream。

bson_csv_adapter.hpp

#ifndef BSON_CSV_ADAPTER_HPP_IUPAHOIUHASDUIKHLKHAD
#define BSON_CSV_ADAPTER_HPP_IUPAHOIUHASDUIKHLKHAD

#include <bsoncxx/types.hpp>

#include <ostream>

class BsonCSVadapter {
public:
    // construct from a bsoncxx::document::view
    explicit BsonCSVadapter(bsoncxx::document::view&& bdv) : m_bdv(std::move(bdv)) {}

    std::ostream& print(std::ostream& os) const {
        print_view(os, m_bdv);
        return os << '\n';
    }

private:
    void print_view(std::ostream& os, const bsoncxx::document::view& v) const {
        print_range(os, v.begin(), v.end());
    }

    template<typename It>
    void print_range(std::ostream& os, It begin, It end) const {
        if(begin != end) {
            print_element(os, *begin);
            for(++begin; begin != end; ++begin) {
                os << ',';
                print_element(os, *begin);
            }
        }
    }

    // bsoncxx::document::element or bsoncxx::array::element
    template<typename ElType>
    void print_element(std::ostream& os, const ElType& e) const {
        // os << e.key().to_string() << ':';        // if you want the fields key name

        switch(e.type()) { // bsoncxx::type
            case bsoncxx::type::k_double:
                os << e.get_double();
                break;

            case bsoncxx::type::k_int32:
                os << e.get_int32();
                break;

            case bsoncxx::type::k_utf8: {
                bsoncxx::stdx::string_view sv = e.get_utf8();
                os << sv.data();
                break;
            }
            case bsoncxx::type::k_array: {
                const bsoncxx::array::view& av = e.get_array();
                print_view(os, av);
                break;
            }
            case bsoncxx::type::k_document: {
                const bsoncxx::document::view& dv = e.get_document();
                print_view(os, dv);
                break;
            }
        }
    }

    bsoncxx::document::view m_bdv;
};

// operator to support streaming
std::ostream& operator<<(std::ostream& os, const BsonCSVadapter& a) {
    return a.print(os);
}

#endif

然后在您的.cpp 文件中：

#include "bson_csv_adapter.hpp"

        // ...
        if(maybe_result) {
            // stream to std::cout
            std::cout << BsonCSVadapter(*maybe_result);

            // stream to a file
            std::ofstream myfile("newtest.csv");
            myfile << BsonCSVadapter(*maybe_result);
        }

输出：

5f2a435186ff70fb16f873ec,Gutta,sumanth,25,active,sumanth@gmail.com

如果您取消注释 os << e.key().to_string() << ':'; 行，您将获得以下输出：

_id:$oid:5f2a435186ff70fb16f873ec,first_name:Gutta,last_name:sumanth,age:25,employee_status:active,email:sumanth@gmail.com