案例：超市商品管理

该案例是北大青鸟《使用C#语言开发数据库应用系统》第8章的项目案例，这是我自己的做的，给大家参考参考，有什么不足之处，还望各位前辈多多指点！

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Data;
using System.Data.SqlClient;
using System.Configuration;
using System.Windows.Forms;

namespace SuperCommodityManager
{
    public class DBHelper
    {
        //通过读取配置文件获得连接字符串
        private static readonly string connString = ConfigurationManager.ConnectionStrings[“strConn“].ToString（）;

        //创建Connection对象
        private SqlConnection conn;
        public SqlConnection Conn
        {
            get
            {
                if （conn == null）
                {
                    conn = new SqlConnection（connString）;
                }
                return conn;
            }
            set { conn = value; }
        }

        //打开连接
        public void OpenConnection（）
        {
            if （conn.State == ConnectionState.Closed）
            {
                conn.Open（）;
            }
            if （conn.State == ConnectionState.Broken）
            {
                conn.Close（）;
                conn.Open（）;
            }
        }

        //关闭连接
        public void CloseConnection（）
        {
            if （conn.State == ConnectionState.Open || conn.State == ConnectionState.Broken）
            {
                conn.Close（）;
            }
        }


        /// 

        /// 得到首行首列的值
        /// 

        /// 
        /// 
        public object GetExecuteScalar（string sql）
        {
            SqlCommand comm = new SqlCommand（sql Conn）;
            object data = null;
            try
            {
                OpenConnection（）;   //打开连接
                data = comm.ExecuteScalar（）;    //返回单个值

            }
            catch （Exception ex）
            {
                MessageBox.Show（“出现异常！“ + ex.Message）;
                data = null;
            }
            finally
            {
                CloseConnection（）;  //关闭连接
            }
            return data;
        }

        /// 

        /// 得到受影响行数
        /// 

        /// 
        /// 
        public int GetExecuteNonQuery（string sql）
        {
            SqlCommand comm = new SqlCommand（sql Conn）;
            int num = 0;
            try
            {
                OpenConnection（）;   //打开连接
                num = comm.ExecuteNonQuery（）;   //返回行的语句

            }
            catch （Exception ex）
            {
                MessageBox.Show（“出现异常！“ + ex.Message）;
            }
            finally
            {
                CloseConnection（）;  //关闭连接
            }
            return num;
        }

        /// 

        /// 得到多行多列的值
        /// 

        /// 
        /// 
        public SqlDataReader GetExecuteReader（string sql）
        {
            S

 属性            大小     日期    时间   名称
----------- ---------  ---------- -----  ----

     文件       6926  2011-12-29 23:03  SuperCommodityManager\SuperCommodityManager\obj\x86\Debug\SuperCommodityManager.csproj.FileListAbsolute.txt

     文件     234496  2011-12-29 23:03  SuperCommodityManager\SuperCommodityManager\bin\Debug\SuperCommodityManager.exe

     文件     234496  2011-12-29 23:03  SuperCommodityManager\SuperCommodityManager\obj\x86\Debug\SuperCommodityManager.exe

     文件      11600  2011-12-29 23:03  SuperCommodityManager\SuperCommodityManager\bin\Debug\SuperCommodityManager.vshost.exe

     文件       4440  2011-12-28 13:50  SuperCommodityManager\SuperCommodityManager\obj\x86\Debug\DesignTimeResolveAssemblyReferences.cache

     文件       6600  2011-12-29 23:03  SuperCommodityManager\SuperCommodityManager\obj\x86\Debug\DesignTimeResolveAssemblyReferencesInput.cache

     文件       8609  2011-12-28 15:10  SuperCommodityManager\SuperCommodityManager\obj\x86\Debug\ResolveAssemblyReference.cache

     文件        225  2011-12-28 16:41  SuperCommodityManager\SuperCommodityManager\App.config

     文件        225  2011-12-28 16:41  SuperCommodityManager\SuperCommodityManager\bin\Debug\SuperCommodityManager.exe.config

     文件        225  2011-12-28 16:41  SuperCommodityManager\SuperCommodityManager\bin\Debug\SuperCommodityManager.vshost.exe.config

     文件       1386  2011-12-27 08:27  SuperCommodityManager\SuperCommodityManager\Properties\AssemblyInfo.cs

     文件       3571  2011-12-27 08:31  SuperCommodityManager\SuperCommodityManager\DBHelper.cs

     文件        952  2011-12-28 17:33  SuperCommodityManager\SuperCommodityManager\FrmAbout.cs

     文件       4533  2011-12-28 17:33  SuperCommodityManager\SuperCommodityManager\FrmAbout.Designer.cs

     文件       4871  2011-12-28 14:50  SuperCommodityManager\SuperCommodityManager\FrmCommodityList.cs

     文件      15212  2011-12-28 00:55  SuperCommodityManager\SuperCommodityManager\FrmCommodityList.Designer.cs

     文件       3778  2011-12-28 16:31  SuperCommodityManager\SuperCommodityManager\FrmCommoditySort.cs

     文件       9067  2011-12-28 16:27  SuperCommodityManager\SuperCommodityManager\FrmCommoditySort.Designer.cs

     文件       3703  2011-12-28 16:26  SuperCommodityManager\SuperCommodityManager\FrmEditCommoditySort.cs

     文件       4477  2011-12-28 16:17  SuperCommodityManager\SuperCommodityManager\FrmEditCommoditySort.Designer.cs

     文件       7281  2011-12-28 16:27  SuperCommodityManager\SuperCommodityManager\FrmEditGoodsInfo.cs

     文件      10653  2011-12-28 00:21  SuperCommodityManager\SuperCommodityManager\FrmEditGoodsInfo.Designer.cs

     文件       3220  2011-12-27 10:33  SuperCommodityManager\SuperCommodityManager\FrmLogin.cs

     文件       6830  2011-12-27 09:39  SuperCommodityManager\SuperCommodityManager\FrmLogin.Designer.cs

     文件       4046  2011-12-28 16:34  SuperCommodityManager\SuperCommodityManager\FrmModifyPwd.cs

     文件       6430  2011-12-27 12:00  SuperCommodityManager\SuperCommodityManager\FrmModifyPwd.Designer.cs

     文件       2493  2011-12-28 15:37  SuperCommodityManager\SuperCommodityManager\FrmSuperCommodity.cs

     文件       9541  2011-12-28 15:37  SuperCommodityManager\SuperCommodityManager\FrmSuperCommodity.Designer.cs

     文件        505  2011-12-28 16:41  SuperCommodityManager\SuperCommodityManager\Program.cs

     文件       2890  2011-12-27 08:27  SuperCommodityManager\SuperCommodityManager\Properties\Resources.Designer.cs

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