public void Save_Using_Update() { var rentals = new RealEstateContext().Database.GetCollection <Rental>("rentals"); var rental = new Rental(); rental.Id = ObjectId.GenerateNewId().ToString(); rentals.Save(rental); var query = Query.EQ("_id", ObjectId.Parse(rental.Id)); var update = Update.Replace(rental); rentals.Update(query, update, UpdateFlags.Upsert); Console.WriteLine("Query Document:"); Console.WriteLine(query); Console.WriteLine("Update Document:"); Console.WriteLine(update.ToJson()); }