public static FxFunction GetInstance()
        {
            if (_instance == null)
            {
                _instance = new FxFunction();
            }

            return _instance;
        }
        private void button_get_products_Click(object sender, EventArgs e)
        {
            FxFunction fx = FxFunction.GetInstance();

            dataGridView.DataSource = fx.GetData("Select * from Products");
        }
        private void Form1_Load(object sender, EventArgs e)
        {
            FxFunction fx = FxFunction.GetInstance();

            dataGridView.DataSource = fx.GetData("Select * from Categories");
        }