IMongoCollection
     
       _collect;                        string mongoDB_Host = ConfigurationManager.AppSettings["MongoDB"].ToString();                        string mongoDB_DbName = ConfigurationManager.AppSettings["MongoDB_DBNAME"].ToString();                        MongoDB.Driver.MongoClient mc = new MongoClient(mongoDB_Host);                        IMongoDatabase _db = mc.GetDatabase(mongoDB_DbName);                        _collect = _db.GetCollection
      
       (TableName);                        BsonDocument dbMatch = new BsonDocument { { "Day", new BsonDocument("$eq", Day) }, { "StartTime", new BsonDocument("$lt", StartTime) } };                        BsonDocument dbGroup = new BsonDocument { { "_id", "$EmployeeId" }, { "maxStartTime", new BsonDocument("$max", "$StartTime") } };                        var aggregate = _collect.Aggregate().Match(dbMatch).Group(dbGroup);                        List
       
         list222 = aggregate.ToList
        
         ();                        if (list222 != null && list222.Count > 0)                        {                            // NLogger.Error("分组总和：--   " + list222.Count);                            foreach (var itt in list222)                            {                                gUserLocation g = new gUserLocation();                                g.EmployeeId = Convert.ToInt32(itt["_id"].ToString());                                g.StartTime = Convert.ToInt64(itt["maxStartTime"].ToString());                                gUserLocationlist.Add(g);                            }                        }
        
       
      
     

　　参考：

http://www.cnblogs.com/shaosks/p/5816932.html

http://www.cnblogs.com/lizeyan/p/5411708.html

http://blog.csdn.net/shiyaru1314/article/details/52442957