Aggregate in Mongodb in C#

Filter record from collection “OperationSession”, sort by “WorldId” descending, then group by “WorldId”, then pick first record from each group, then sort result:

Way #1:

db.getCollection('OperationSession').aggregate(
[
  { "$match": {"ActivityId":74,"GameId":2109} },
  { "$sort":{ "CreateTime" : -1} },
  { "$group":
    { 
        _id:"$WorldId",
        SessionId:{"$first": "$_id" },
        GameId:{"$first": "$GameId" },
        WorldId:{"$first": "$WorldId" },
        ActivityId:{"$first": "$ActivityId" },
        Type:{"$first": "$Type" },
        Status:{"$first": "$Status" },
        ActivityStatus:{"$first": "$ActivityStatus" }
     }
   },
   { "$sort":{ "WorldId" : 1} },
   { "$skip": 20},
   { "$limit": 10}
  ]
)

Way #2:

db.OperationSession.aggregate()
      .match({"ActivityId":74,"GameId":2109})
      .sort({"CreateTime":-1})
      .group({
            "_id":"$WorldId",
            "SessionId":{"$first": "$_id" },
            "GameId":{"$first": "$GameId" },
            "WorldId":{"$first": "$WorldId" },
            "ActivityId":{"$first": "$ActivityId" },
            "Type":{"$first": "$Type" },
            "Status":{"$first": "$Status" },
            "ActivityStatus":{"$first": "$ActivityStatus" }
        })
      .sort({"WorldId":1})
      .skip(20)
      .limit(10)

In C#:

collection.Aggregate<DataEntity.OperationSession>()
                .Match(s => s.ActivityId == 74 && s.GameId == 2109)
                .SortByDescending(s => s.CreateTime)
                .Group(
                    s => s.WorldId,
                    s => new Interface.OperationSession
                    {
                        SessionId = s.Select(x => x.Id).First(),
                        GameId = s.Select(x => x.GameId).First(),
                        WorldId = s.Select(x => x.WorldId).First(),
                        ActivityId = s.Select(x => x.ActivityId).First(),
                        Type = s.Select(x => x.Type).First(),
                        Status = s.Select(x => x.Status).First(),
                        ActivityStatus = s.Select(x => x.ActivityStatus).First()
                    })
                .SortBy(s => s.WorldId)
                .Skip(20)
                .Limit(10).ToList();