SqlHelp类

public class SqlHelp
    {
        private static SqlConnection conn = new SqlConnection();
        private static SqlCommand cmd = new SqlCommand();
        private static string connstr = ConfigurationManager.ConnectionStrings["ConnectionString"].ConnectionString;
        /// <summary>
        /// 打开连接
        /// </summary>
        private static void openConnection()
        {
            if (conn.State == ConnectionState.Closed)
            {
                try
                {
                    conn.ConnectionString = connstr;
                    cmd.Connection = conn;
                    conn.Open();
                }
                catch (Exception e)
                {

                    throw new Exception(e.Message);
                }

            }
        }
        /// <summary>
        /// 关闭连接
        /// </summary>
        private static void closeConnection()
        {
            if (conn.State == ConnectionState.Open)
            {
                conn.Close();
            }
            conn.Dispose();
            cmd.Dispose();
        }

        /// <summary>
        /// 执行查询语句
        /// </summary>
        /// <param name="sql">sql查询语句</param>
        public static void ExecuteSql(string sql)
        {
            try
            {
                openConnection();
                cmd.CommandType = CommandType.Text;
                cmd.CommandText = sql;
                cmd.ExecuteNonQuery();

            }
            catch (Exception e)
            {

                throw new Exception(e.Message);
            }
            finally
            {
                closeConnection();
            }
        }
        /// <summary>
        /// 查询获得数据集
        /// </summary>
        /// <param name="sql">输入查询的sql语句</param>
        /// <returns>返回数据集</returns>
        public static DataSet GetDataSet(string sql)
        {
            SqlDataAdapter sda = new SqlDataAdapter();
            DataSet ds = new DataSet();
            try
            {
                openConnection();
                cmd.CommandType = CommandType.Text;
                cmd.CommandText = sql;
                sda.SelectCommand = cmd;
                sda.Fill(ds);

            }
            catch (Exception e)
            {

                throw new Exception(e.Message);
            }
            finally
            {
                closeConnection();
            }
            return ds;
        }
        /// <summary>
        /// 获得数据视图
        /// </summary>
        /// <param name="sql">输入sql查询语句</param>
        /// <returns></returns>
        public static DataView GetDataView(string sql)
        {
            SqlDataAdapter sda = new SqlDataAdapter();
            DataView dv = new DataView();
            DataSet ds = new DataSet();
            try
            {
                openConnection();
                cmd.CommandType = CommandType.Text;
                cmd.CommandText = sql;
                sda.SelectCommand = cmd;
                sda.Fill(ds);
                dv = ds.Tables[0].DefaultView;

            }
            catch (Exception e)
            {

                throw new Exception(e.Message);
            }
            finally
            {
                closeConnection();
            }
            return dv;
        }
    }