test/DB.cs

using MySql.Data.MySqlClient;
using System.Data;

namespace NeshinaPolina07_11
{
    internal class DB
    {
        private static DB instance;
        private readonly string connectionString = "server=git.pgk.alspio.com; port=3306; username=ISP41_Zvyagintsev; password = ISP41_Zvyagintsev;database=ISP41_Zvyagintsev; SslMode=none";

        private MySqlConnection connection;

        private DB()
        {
            connection = new MySqlConnection(connectionString);
            OpenConnection();
        }

        public static DB GetInstance()
        {
            if (instance == null)
                instance = new DB();
            return instance;
        }

        public void OpenConnection()
        {
            if (connection.State == ConnectionState.Closed)
                connection.Open();
        }

        public void CloseConnection()
        {
            if (connection.State == ConnectionState.Open)
                connection.Close();
        }

        public MySqlConnection GetConnection() => connection;
    }
}