sqlhelper里面数据库连接要如何写才最好

using System;using System.Collections.Generic;using System.Linq;using System.Text;using System.Data;using System.Data.OleDb;using System.Configuration;using System.Data.SqlClient;using System.Data.Sql;namespace WorkDAL{    public class SqlHelper    {        /// 连接字符串        public static readonly string ConnectionString = ConfigurationSettings.AppSettings["StrCon"].ToString();        SqlConnection con = new SqlConnection(ConfigurationSettings.AppSettings["StrCon"].ToString());        //用于缓存参数的HASH表        //private static Hashtable parmCache = Hashtable.Synchronized(new Hashtable());        /// <returns>执行命令所影响的行数</returns>        public static int ExecuteNonQuery(SqlConnection connection, string cmdText, params SqlParameter[] commandParameters)        {            SqlCommand cmd = new SqlCommand();            PrepareCommand(cmd, connection, cmdText, commandParameters);            int val = cmd.ExecuteNonQuery();            cmd.Parameters.Clear();            return val;        }        /// <summary>        /// 用执行的数据库连接执行一个返回数据集的sql命令        /// </summary>        /// <remarks>        /// 举例:          ///  OleDbDataReader r = ExecuteReader(connString, "PublishOrders", new OleDbParameter("@prodid", 24));        /// </remarks>        /// <param name="connectionString">一个有效的连接字符串</param>        /// <param name="commandText">存储过程名称或者sql命令语句</param>        /// <param name="commandParameters">执行命令所用参数的集合</param>        /// <returns>包含结果的读取器</returns>        /// <summary>        /// 返回一个DataSet数据集        /// </summary>        /// <param name="connectionString">一个有效的连接字符串</param>        /// <param name="cmdText">存储过程名称或者sql命令语句</param>        /// <param name="commandParameters">执行命令所用参数的集合</param>        /// <returns>包含结果的数据集</returns>        /// <summary>        /// 用指定的数据库连接字符串执行一个命令并返回一个数据集的第一列        /// </summary>        /// <remarks>        ///例如:          ///  Object obj = ExecuteScalar(connString, "PublishOrders", new OleDbParameter("@prodid", 24));        /// </remarks>        ///<param name="connectionString">一个有效的连接字符串</param>        /// <param name="commandText">存储过程名称或者sql命令语句</param>        /// <param name="commandParameters">执行命令所用参数的集合</param>        /// <returns>用 Convert.To{Type}把类型转换为想要的 </returns>        public static object ExecuteScalar(string connectionString, string cmdText, params SqlParameter[] commandParameters)        {            SqlCommand cmd = new SqlCommand();            using (SqlConnection connection = new SqlConnection(connectionString))            {                PrepareCommand(cmd, connection, cmdText, commandParameters);                object val = cmd.ExecuteScalar();                cmd.Parameters.Clear();                return val;            }        }        /// <summary>        /// 用指定的数据库连接执行一个命令并返回一个数据集的第一列        /// </summary>        /// <remarks>        /// 例如:          ///  Object obj = ExecuteScalar(connString, "PublishOrders", new OleDbParameter("@prodid", 24));        /// </remarks>        /// <param name="conn">一个存在的数据库连接</param>        /// <param name="commandText">存储过程名称或者sql命令语句</param>        /// <param name="commandParameters">执行命令所用参数的集合</param>        /// <returns>用 Convert.To{Type}把类型转换为想要的 </returns>        public static object ExecuteScalar(SqlConnection connection, string cmdText, params SqlParameter[] commandParameters)        {            SqlCommand cmd = new SqlCommand();            PrepareCommand(cmd, connection, cmdText, commandParameters);            object val = cmd.ExecuteScalar();            cmd.Parameters.Clear();            return val;        }            /// <summary>        /// 准备执行一个命令        /// </summary>        /// <param name="cmd">sql命令</param>        /// <param name="conn">Sql连接</param>        /// <param name="trans">Sql事务</param>        /// <param name="cmdText">命令文本,例如：Select * from Products</param>        /// <param name="cmdParms">执行命令的参数</param>        private static void PrepareCommand(SqlCommand cmd, SqlConnection conn, string cmdText, SqlParameter[] cmdParms)        {            //判断连接的状态。如果是关闭状态，则打开            if (conn.State != ConnectionState.Open)                conn.Open();            //cmd属性赋值            cmd.Connection = conn;            cmd.CommandText = cmdText;            cmd.CommandType = CommandType.Text;            //添加cmd需要的存储过程参数            if (cmdParms != null)            {                foreach (SqlParameter parm in cmdParms)                    cmd.Parameters.Add(parm);            }        }        /// <summary>        /// 分页使用        /// </summary>        /// <param name="query"></param>        /// <param name="passCount"></param>        /// <returns></returns>        private static string recordID(string query, int passCount)        {            using (SqlConnection m_Conn = new SqlConnection(ConnectionString))            {                m_Conn.Open();                SqlCommand cmd = new SqlCommand(query, m_Conn);                string result = string.Empty;                using (SqlDataReader dr = cmd.ExecuteReader())                {                    while (dr.Read())                    {                        if (passCount < 1)                        {                            result += "," + dr.GetInt32(0);                        }                        passCount--;                    }                }                m_Conn.Close();                m_Conn.Dispose();                return result.Substring(1);            }        }        /// <summary>        /// ACCESS高效分页        /// </summary>        /// <param name="pageIndex">当前页码</param>        /// <param name="pageSize">分页容量</param>        /// <param name="strKey">主键</param>        /// <param name="showString">显示的字段</param>        /// <param name="queryString">查询字符串，支持联合查询</param>        /// <param name="whereString">查询条件，若有条件限制则必须以where 开头</param>        /// <param name="orderString">排序规则</param>        /// <param name="pageCount">传出参数：总页数统计</param>        /// <param name="recordCount">传出参数：总记录统计</param>        /// <returns>装载记录的DataTable</returns>        public static DataTable ExecutePager(int pageIndex, int pageSize, string strKey, string showString, string queryString, string whereString, string orderString, out int pageCount, out int recordCount)        {            if (pageIndex < 1) pageIndex = 1;            if (pageSize < 1) pageSize = 10;            if (string.IsNullOrEmpty(showString)) showString = "*";            if (string.IsNullOrEmpty(orderString)) orderString = strKey + " asc ";            using (OleDbConnection m_Conn = new OleDbConnection(ConnectionString))            {                m_Conn.Open();                string myVw = string.Format(" ( {0} ) tempVw ", queryString);                OleDbCommand cmdCount = new OleDbCommand(string.Format(" select count(*) as recordCount from {0} {1}", myVw, whereString), m_Conn);                recordCount = Convert.ToInt32(cmdCount.ExecuteScalar());                if ((recordCount % pageSize) > 0)                    pageCount = recordCount / pageSize + 1;                else                    pageCount = recordCount / pageSize;                OleDbCommand cmdRecord;                if (pageIndex == 1)//第一页                {                    cmdRecord = new OleDbCommand(string.Format("select top {0} {1} from {2} {3} order by {4} ", pageSize, showString, myVw, whereString, orderString), m_Conn);                }                else if (pageIndex > pageCount)//超出总页数                {                    cmdRecord = new OleDbCommand(string.Format("select top {0} {1} from {2} {3} order by {4} ", pageSize, showString, myVw, "where 1=2", orderString), m_Conn);                }                else                {                    int pageLowerBound = pageSize * pageIndex;                    int pageUpperBound = pageLowerBound - pageSize;                    string recordIDs = recordID(string.Format("select top {0} {1} from {2} {3} order by {4} ", pageLowerBound, strKey, myVw, whereString, orderString), pageUpperBound);                    cmdRecord = new OleDbCommand(string.Format("select {0} from {1} where {2} in ({3}) order by {4} ", showString, myVw, strKey, recordIDs, orderString), m_Conn);                }                OleDbDataAdapter dataAdapter = new OleDbDataAdapter(cmdRecord);                DataTable dt = new DataTable();                dataAdapter.Fill(dt);                m_Conn.Close();                m_Conn.Dispose();                return dt;            }        }        //////////////////////////////////////////////////添加的方法///////////////////////////////        /// <summary>        /// 根据数据库连接字符串,创建数据库连接对象        /// </summary>        /// <param name="connectionString">数据库连接字符串</param>        /// <returns>数据库连接对象</returns>                public static SqlConnection CreateDbConnection(string connectionString)        {            return new SqlConnection(connectionString);        }