在mongocxx中以字符串形式运行聚集率查询

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

int main() {
    mongocxx::instance instance{}; // 初始化mongocxx驱动

    mongocxx::client client{mongocxx::uri{}}; // 连接MongoDB数据库

    mongocxx::database db = client["mydb"]; // 获取数据库

    mongocxx::collection coll = db["mycollection"]; // 获取集合

    bsoncxx::builder::stream::document pipeline_builder;
    pipeline_builder << "$group" << bsoncxx::builder::stream::open_document
                     << "_id" << "$field1" << "count" << bsoncxx::builder::stream::open_document
                     << "$sum" << 1 << bsoncxx::builder::stream::close_document
                     << bsoncxx::builder::stream::close_document;

    bsoncxx::document::value pipeline = pipeline_builder << bsoncxx::builder::stream::finalize;

    mongocxx::options::aggregate options;
    options.pipeline(std::move(pipeline));

    auto result = coll.aggregate(options); // 执行聚集率查询

    for (auto&& doc : result) {
        std::cout << bsoncxx::to_json(doc) << std::endl; // 输出查询结果
    }

    return 0;
}