C#如何向MongoDB GridFs中存储文件

var server = MongoServer.Create("mongodb://localhost:27020");
var database = server.GetDatabase("tesdb");

var fileName = "D:\\Untitled.png";
var newFileName = "D:\\new_Untitled.png";
using (var fs = new FileStream(fileName, FileMode.Open))
{
var gridFsInfo = database.GridFS.Upload(fs, fileName);
var fileId = gridFsInfo.Id;

ObjectId oid= new ObjectId(fileId);
var file = database.GridFS.FindOne(Query.EQ("_id", oid));

using (var stream = file.OpenRead())
{
var bytes = new byte[stream.Length];
stream.Read(bytes, 0, (int)stream.Length);
using(var newFs = new FileStream(newFileName, FileMode.Create))
{
newFs.Write(bytes, 0, bytes.Length);
}
}
}