asp.net的一个dbhelper类

using System;
using System.Collections;
using System.Collections.Specialized;
using System.Data;
using System.Data.SqlClient;
using System.Configuration;
using System.Collections.Generic;
using System.Text;
namespace Maticsoft.DBUtility
{
     /// <summary>
     /// Copyright (C) 2004-2008 
     /// 数据访问基础类(基于SQLServer)
     /// 用户可以修改满足自己项目的需要。
     /// </summary>
     public abstract class DbHelperSQL
    {
           //数据库连接字符串(web.config来配置)
           //<add key="ConnectionString" value="server=127.0.0.1;database=DATABASE;uid=sa;pwd=" />  
            protected static string connectionString = System.Configuration.ConfigurationManager.AppSettings["ConnectionString"].ToString();
            public DbHelperSQL()
           {   
           }
           #region 公用方法
           public static int GetMaxID(string FieldName,string TableName)
           {
                 string strsql = "select max(" + FieldName + ")+1 from " + TableName;
                 object obj = GetSingle(strsql);
                 if (obj == n