[C#] update datatable ที่อยู่ใน datagridview ที่ยังไม่ถูกเพิ่มลงในฐานข้อมูล

        public DataTable myDataTable;
        private void button1_Click(object sender, EventArgs e)
        {
            if (myDataTable == null)
            {
                myDataTable = new DataTable();
                myDataTable.Columns.Add(new DataColumn("CatCode", typeof(string)));
                myDataTable.Columns.Add(new DataColumn("BalStock", typeof(string)));

                DataColumn[] pk = new DataColumn[1];
                pk[0] = myDataTable.Columns["CatCode"];
                myDataTable.PrimaryKey = pk;

                myDataTable.Rows.Add(new object[] { "1", "50" });
                myDataTable.Rows.Add(new object[] { "2", "20" });

                dataGridView1.DataSource = myDataTable;
            }
            else
            {   
                DataRow newrow = myDataTable.NewRow();
                newrow["CatCode"] = (myDataTable.Rows.Count + 1).ToString();

                // Do your calculation for the second column value (BalStock) 
                newrow["BalStock"] = "100";

                myDataTable.Rows.Add(newrow);
                myDataTable.AcceptChanges();

                dataGridView1.DataSource = myDataTable;
            }
        }