基于ado.net访问sql server数据库的sqlhelper

 /// <summary>
    ///  访问SQL Server的通用数据访问类
    /// </summary>
    class SQLHelper
    {
        //定义连接字符串
        private static readonly string connString =
            ConfigurationManager.ConnectionStrings["connString"].ToString();
        /// <summary>
        /// 执行增删改操作
        /// </summary>
        /// <param name="sql"></param>
        /// <returns></returns>
        public static int Update(string sql)
         {
            SqlConnection conn = new SqlConnection(connString);
            SqlCommand cmd = new SqlCommand(sql, conn);
             try
              {
                conn.Open();
                return  cmd.ExecuteNonQuery();
               }
              catch(Exception  ex)
              {
                //将异常信息写入日志
                throw ex;
               }
              finally//最终一定会被执行的代码
             {
                conn.Close();