为数据库连接写的封装类

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

namespace Windowscontrol//工程名
{
    class OperateDB//数据库名
    {
        public static string connectionString = "Server=WIN-41J9I28H5RO;Integrated Security=True;DataBase=certifDB";
        SqlConnection conn = new SqlConnection(connectionString);
        /// <summary>
        /// 返回数据集
        /// </summary>
        /// <param name="sqlstring"> sql语句</param>
        /// <param name="tableName"> 虚拟表的名字</param>
        /// <returns>返回dataset对象</returns>
        public DataSet GetDataSet(string sqlstring, string tableName)
        {
            try
            {
                conn.Open();
                SqlCommand mycomm = new SqlCommand(sqlstring, conn);
                SqlDataAdapter myda = new SqlDataAdapter(mycomm);
                DataSet myds = new DataSet();
                myda.Fill(myds, tableName);
                return myds;
               
            }          
            finally
            {
                if (conn.State == ConnectionState.Open)
                    conn.Close();
            }
        }
        #region open
        /// <summary>
        /// 打开数据库连接
        /// </summary>
        private void Open()
        {
            if (conn == null)
            {
                conn = new SqlConnection(connectionString);
            }
            if (conn.State == ConnectionState.Closed)
            {
                conn.Open();
            }
        }
        #endregion
        #region close
        /// <summary>
        /// 关闭连接
        /// </summary>
        public void close()
        {
            if (conn != null && conn.State != ConnectionState.Closed)
            {
                conn.Close();
            }
        }
        #endregion
        #region Dispose
        /// <summary>
        /// 释放数据库连接资源
        /// </summary>
        public void Dispose()
        {
            if(conn!=null)
            {
                conn.Dispose();
                conn = null;
            }
        }
        #endregion
        #region
        /// <summary>
        /// 执行SqlCommand命令
        /// </summary>
        /// <param name="sqlstring">sql语句</param>
        /// <returns></returns>
        public int ExecuteSql(string sqlstring)
        {                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   
            this.Open();
            SqlCommand com = new SqlCommand(sqlstring, conn);
            int n = com.ExecuteNonQuery();
            this.close();
            return n;
        }
        #endregion
        #region
        /// <summary>
        /// 创建SqlDataReader对象
        /// </summary>
        /// <param name="sqlstring">select语句</param>
        /// <returns>返回SqlDataReader对象</returns>
        public SqlDataReader GetDataReader(string sqlstring)
        {
                conn.Open();
                SqlCommand com = new SqlCommand(sqlstring, conn);
                SqlDataReader dr = com.ExecuteReader(CommandBehavior.CloseConnection);
                return dr;
        }
        #endregion
    }
}