我的数据库封装类C# Sqlserver

using System;
using System.Data;
using System.Configuration;
using System.Web;
//using System.Web.Security;
//using System.Web.UI;
//using System.Web.UI.WebControls;
//using System.Web.UI.WebControls.WebParts;
//using System.Web.UI.HtmlControls;
using System.Data.SqlClient;
using System.Text;
using System.Collections;
namespace mySqlSQLDB
{

    public class DbAccess
    {
        SqlConnection conn = null;
        SqlCommand cmd = null;
        public DbAccess()
        {
            //
            // TODO: 在此处添加构造函数逻辑
            //
            conn = new SqlConnection();
            conn.ConnectionString = Convert.ToString(System.Configuration.ConfigurationSettings.AppSettings["datasource"]);
            //conn.ConnectionString = "initial catalog=_new;data source=.;user id=bt;password=btbtbtbt;Connect Timeout=5000";
            cmd = new SqlCommand();
            cmd.Connection = conn;
            cmd.CommandTimeout = 0;
    
        }
        public DbAccess(string constr)
        {
            //
            // TODO: 在此处添加构造函数逻辑
            //
            co