如何从 c# 计算 mongodb 中带有过滤器的文档

Question

I am trying to make this email validation thing with c# and mongodb, but i don't know how am i suppose to count the documents with a filter in mongoDB? 有什么想法吗？ 到目前为止，这是我的代码

public ActionResult Saveuserinput(string firstname, string lastname, string dob, string studentid, string gender, string email, string phonenumber, string address, string city, string zipcode, string state,string password)
        {
            ViewData["message"] = $"Account created";
            var client = new MongoClient("connection string");
            var database = client.GetDatabase("AccountInfo");
            var collec = database.GetCollection<BsonDocument>("AccountInfo");

            var filter = Builders<BsonDocument>.Filter.Eq("Email", email);
            var Userinfo = collec.Find(filter).First();

            int avalibility = collec.CountAsync(filter);
            if (avalibility > 1)
            {
               return Content("Email Taken");
            }

            else
            {
                 var document = new BsonDocument
            {
                {"Firstname", firstname },
                {"Lastname", lastname },
                {"Date of birth", dob },
                {"Student ID", studentid },
                {"Gender", gender },
                {"Email", email },
                {"Password", password },
                {"Phone number", phonenumber },
                {"Address", address },
                {"City", city },
                {"Zipcode", zipcode },
                {"State", state }
            };

                collec.InsertOneAsync(document);
                return View("~/Views/SignIn/Index.cshtml");
            }

Answer 1

在应用过滤器后，这可以很好地获取文档数：

var crsr = collection.Find(filter);
var size = crsr.CountDocuments();
Console.WriteLine(size); // prints the document count