如何在C ++中使用MongoDB GeoSpatial索引 [英] How to use MongoDB GeoSpatial Index in C++

问题描述

在python中，pymongo为MongoDB GeoSpatial索引提供了很好的支持.但是，对于C ++，当我在C ++中使用mongocxx时，我对语法有些困惑.

In python, pymongo provides nice support for MongoDB GeoSpatial index. However, for C++ when I use mongocxx in C++, I am a little bit confused about the grammar.

例如，在我使用的python(pymongo)中

For example, in python (pymongo) I used

cursor = db.colection.find(
    {
        "loc": {
            "$near": [lon, lat]
        }
    }
).limit(10)

以获取给定位置的最近10件商品.但是我该如何在C ++中做同样的事情?

to get nearest 10 items for given location. But how can I do the same thing in C++?

我尝试过:

mongocxx::cursor cursor = coll.find(document{} << "loc" << open_document <<
                                    "$near" << [lon, lat]
                                    << close_document << finalize);

我不确定这是否正确，我无法设置结果数.

I am not sure if this is correct approach, and I failed to set the number of results.

有人可以给我一些有关C ++中的GeoSpatial索引的说明吗?文档/示例将被高度重视.

Could anyone give me some instructions on GeoSpatial index in C++? Documents/examples will be highly apreciated.

非常感谢.

推荐答案

您可以使用 mongocxx::collection::find .以下应该工作:

You can use mongocxx::options::find::limit. Check also mongocxx::collection::find. The following should work :

mongocxx::options::find opts;
opts.limit(10);

mongocxx::cursor cursor = coll.find(document{} << "loc" << open_document 
    << "$near" << bsoncxx::builder::stream::open_array 
    << lon << lat << bsoncxx::builder::stream::close_array 
    << close_document << finalize, opts);

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