Mongocxx:如何反向显示文档

Mongocxx: How to display the documents inversely

本文关键字：显示 文档 何反 Mongocxx      更新时间：2023-10-16

我试图反向显示集合的文档。在shell中，这可以通过使用以下命令来完成:

db.testcollection.find().sort({$natural:-1})

在文档中我发现了这个函数:

void sort(bsoncxx::document::view_or_value ordering); 

/// The order in which to return matching documents. If $orderby also exists in the modifiers
/// document, the sort field takes precedence over $orderby.
///
/// @param ordering
///   Document describing the order of the documents to be returned.
///
/// @see http://docs.mongodb.org/manual/reference/method/cursor.sort/

如何像shell示例一样将自然值设置为-1 ?谢谢!

您需要使用bsoncxx构建器创建排序顺序文档。下面是插入10个文档并按倒序转储它们的示例:

#include <iostream>
#include <bsoncxx/builder/stream/document.hpp>
#include <bsoncxx/document/value.hpp>
#include <bsoncxx/document/view.hpp>
#include <bsoncxx/json.hpp>
#include <mongocxx/client.hpp>
#include <mongocxx/collection.hpp>
#include <mongocxx/instance.hpp>
#include <mongocxx/options/find.hpp>
#include <mongocxx/uri.hpp>
using namespace bsoncxx;
int main() {
    auto inst = mongocxx::instance{};
    auto client = mongocxx::client{mongocxx::uri{}};
    auto coll = client["test"]["sorttest"];
    coll.drop();
    for (auto i = 0; i < 10; i++) {
        coll.insert_one(builder::stream::document{} << "seq" << i << builder::stream::finalize);
    }
    auto order = builder::stream::document{} << "$natural" << -1 << builder::stream::finalize;
    auto opts = mongocxx::options::find{};
    opts.sort(order.view());
    auto cursor = coll.find({}, opts);
    for (auto&& doc : cursor) {
        std::cout << to_json(doc) << std::endl;
    }
}
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