c# - 如何使用 MongoDb .net 驱动程序获取集合中所有文档的几个特定字段

Question

我正在使用“MongoDB.Driver”版本=“2.9.3”。我试图只请求指定的字段。
我需要执行休耕请求(由 pypline 工作):

db.Segments.find({ "geometry" : { "$nearSphere" : { "$geometry" : { "type" : "Point", "coordinates" : [6.7889999999999997, 64.412599999999998] }, "$minDistance" : 0, "$maxDistance" : 10000 } } }, {_id : 0, 'properties.be_id' : 1,'properties.rel_ltt' : 1 ,'properties.rp_co' : 1, 'properties.wenum' : 1} ).pretty();

我需要创建 Bson 文档，我可以用它来查找具有受限字段的指定数据。
到目前为止，我尝试从 Json 解析为 Bson

var doc = BsonDocument.Parse("{ 'geometry' : { '$nearSphere' : { '$geometry' : { 'type' : 'Point', 'coordinates' :" +
                    " [" + geolocation.Longitude.ToString(culture) + "," + geolocation.Latitude.ToString(culture) + "] }, '$minDistance' : 0, '$maxDistance' : 10 } }}, " +
                    " {'properties.be_id' : 1,'properties.rel_lttr' : 1 ,'properties.rp_co' : 1, 'properties.wenum' : 1}}}");

然后使用查找方法:

SegmentResult.AddRange(RScollection.Find<Segment>(doc).ToList());

这种方法似乎不起作用。
如果有人能帮我解决这个问题，我将不胜感激。

Answer 1

这是一个简单的控制台应用程序。

using MongoDB.Bson;
using MongoDB.Bson.Serialization;
using MongoDB.Driver;
using System.Collections.Generic;
using System.Linq;

public class Program
{           
    public static void Main()
    {
            var tempPipeline = new List<BsonDocument>();

            List<string> selectFields = new List<string>();
            selectFields.Add("<your requested field 1>");
            selectFields.Add("<your requested field 2>");

            var projection = new Dictionary<string, dynamic>();

            //To include fields: Specify the field name and set to 0 in the project document.
            //Ex:- Exclue _id field
            if (!selectFields.Contains("_id"))
            {
                projection.Add("_id", 0);
            }
            //Only the fields specified in the project document are returned. The _id field is returned unless it is set to 0 in the Project document.

            //To include fields: Specify the field name and set to 1 in the project document.

            foreach (var field in selectFields)
            {
                projection.Add(field, 1);       
                //or else
                //projection.Add(field, $"${field}");
            }


            var projectStage = new BsonDocument("$project", projection.ToBsonDocument());
            tempPipeline.Add(projectStage.ToBsonDocument());

            PipelineDefinition<BsonDocument, BsonDocument> aggregatonPipeline = tempPipeline;

            var cursor =  GetDatabase().GetCollection<BsonDocument>("<your collection>").Aggregate(aggregatonPipeline);

           IList<dynamic> results = new List<dynamic>();

            while (cursor.MoveNext())
            {
                foreach (var document in cursor.Current)
                {
                    results.Add(BsonSerializer.Deserialize<dynamic>(document));
                }
            }
            cursor.Dispose();

            results.ToList();
    }

    public static IMongoDatabase GetDatabase()
        {
            var settings = new MongoClientSettings
            {
                // setup your db settings
            };

            var client = new MongoClient(settings);
            return client.GetDatabase("<your database>");
    }
}

阅读更多以设置返回哪些字段: https://docs.mongodb.com/compass/master/query/project/

和更多 :

https://docs.mongodb.com/manual/crud/

https://docs.mongodb.com/manual/tutorial/query-documents/