//1a. kết nối MongoDBLocal
        public string MongoDBLocal_Connect()
        {            
            // Replace the uri string with your MongoDB deployment's connection string.
            var client = new MongoClient(
                "mongodb://localhost:27017/?readPreference=primary&appname=MongoDB%20Compass&directConnection=true&ssl=false"
            );
            var database = client.GetDatabase("HvDadabase");

            return "ok";
        }