public void suamon(string mamon, string tenmon) { var filter = Builders <Mon> .Filter.Eq("mamon", mamon); var updateDef = Builders <Mon> .Update.Set("tenmon", tenmon); Database db = new Database(); this.collection = db.ConnectDB().GetCollection <Mon>("mon"); Mon mon = collection.Find(e => e.mamon == mamon).FirstOrDefault(); var result = collection.UpdateOne(filter, updateDef); }