public static class  SqlHelper    {        public static readonly string connstr =            ConfigurationManager.ConnectionStrings["connstr"].ConnectionString;        public static SqlConnection OpenConnection()        {            SqlConnection conn = new SqlConnection(connstr);            conn.Open();            return conn;        }        public static int ExecuteNonQuery(string cmdText,            params SqlParameter[] parameters)        {            using (SqlConnection conn = new SqlConnection(connstr))            {                conn.Open();                return ExecuteNonQuery(conn, cmdText, parameters);            }        }        public static object ExecuteScalar(string cmdText,            params SqlParameter[] parameters)        {            using (SqlConnection conn = new SqlConnection(connstr))            {                conn.Open();                return ExecuteScalar(conn, cmdText, parameters);            }        }        public static DataTable ExecuteDataTable(string cmdText,            params SqlParameter[] parameters)        {            using (SqlConnection conn = new SqlConnection(connstr))            {                conn.Open();                return ExecuteDataTable(conn, cmdText, parameters);            }        }        public static int ExecuteNonQuery(SqlConnection conn,string cmdText,           params SqlParameter[] parameters)        {            using (SqlCommand cmd = conn.CreateCommand())            {                cmd.CommandText = cmdText;                cmd.Parameters.AddRange(parameters);                return cmd.ExecuteNonQuery();            }        }        public static object ExecuteScalar(SqlConnection conn, string cmdText,            params SqlParameter[] parameters)        {            using (SqlCommand cmd = conn.CreateCommand())            {                cmd.CommandText = cmdText;                cmd.Parameters.AddRange(parameters);                return cmd.ExecuteScalar();            }        }        public static DataTable ExecuteDataTable(SqlConnection conn, string cmdText,            params SqlParameter[] parameters)        {            using (SqlCommand cmd = conn.CreateCommand())            {                cmd.CommandText = cmdText;                cmd.Parameters.AddRange(parameters);                using (SqlDataAdapter adapter = new SqlDataAdapter(cmd))                {                    DataTable dt = new DataTable();                    adapter.Fill(dt);                    return dt;                }            }        }        public static object ToDBValue(this object value)        {            return value =http://www.mamicode.com/= null ? DBNull.Value : value;        }        public static object FromDBValue(this object dbValue)        {            return dbValue =http://www.mamicode.com/= DBNull.Value ? null : dbValue;        }    }