Question

如何使用MongoDB和.NET的C＃驱动程序执行以下操作。

假设我有以下集合（如果存在语法错误则忽略）：

{_id: "2312321321sdd", "Ticker": "AAPL", "CompanyName" : "APPLE", "Viewed": "2013-05-13"}
{_id: "2312321321sde", "Ticker": "AAPL", "CompanyName" : "APPLE", "Viewed": "2013-05-12"}
{_id: "2312321321sdf", "Ticker": "GOOG", "CompanyName" : "GOOGLE", "Viewed": "2013-05-12"}
{_id: "2312321321sdg", "Ticker": "MSFT", "CompanyName" : "MICROSOFT", "Viewed": "2013-05-12"}
{_id: "2312321321sdh", "Ticker": "MSFT", "CompanyName" : "MICROSOFT", "Viewed": "2013-05-11"}

将C＃和/或LINQ与MongoDB驱动程序一起使用，如何获取最新的3个已查看项目以及DISTINCT，因此同一个TICKER没有双倍增加。理想情况下会返回以下内容：

{_id: "2312321321sdd", "Ticker": "AAPL", "CompanyName" : "APPLE", "Viewed": "2013-05-13"}
{_id: "2312321321sdf", "Ticker": "GOOG", "CompanyName" : "GOOGLE", "Viewed": "2013-05-12"}
{_id: "2312321321sdg", "Ticker": "MSFT", "CompanyName" : "MICROSOFT", "Viewed": "2013-05-12"}

提前致谢....

Answer 1

我不能说这要么使用LINQ，要么使用很多C＃，但它是你今天在MongoDB C＃中所追求的。不幸的是，Collection.AsQueryable()不会让你走得太远。

聚合框架或MapReduce是可行的方法。一组不同的代码需要适度，但这里是AF：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using MongoDB.Bson;
using MongoDB.Driver;
using MongoDB.Driver.Linq;

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            MongoCollection<Tick> coll =
                new MongoClient("mongodb://11.11.11.11/test").GetServer()
                                                                .GetDatabase("test")
                                                                .GetCollection<Tick>("tix");

            var group = new BsonDocument
                {
                    {
                        "$group",
                        new BsonDocument
                            {
                                {
                                    "_id",  "$CompanyName"
                                },
                                {
                                    "LastViewed", new BsonDocument
                                        {
                                            {
                                                "$max", "$Viewed"
                                            }
                                        }
                                }
                            }
                    }
                };

            foreach (
                var t in
                    coll.Aggregate(group,
                                   new BsonDocument("$sort", new BsonDocument("LastViewed", -1)),
                                   new BsonDocument("$limit", 3))
                        .ResultDocuments)
            {
                Console.WriteLine("{0} last viewed {1}", t["_id"], t["LastViewed"]);
            }
    }

    public class Tick
    {
        public string Id { get; set; }
        public string Ticker { get; set; }
        public string CompanyName { get; set; }
        public string Viewed { get; set; }
    }
}

MongoDB C＃ - 如何执行以下操作

1 个答案: