public static IDataAccess CreateDataAccess()
        {
            string conStr = ConfigurationManager.ConnectionStrings["connStr"].ToString();
            string conType = ConfigurationManager.ConnectionStrings["connType"].ToString();

            switch (conType)
            {
                case "MSSQL": return new MSSQLDAL(conStr);
                case "ORACLE": return new ORACLEDAL(conStr);
                default:
                    throw new Exception("不支持的类型！");
            }
        }