ADO.net 扩展属性

 public string Nationname
        { 
        get
            {
                string end = "<未填>";
                cmd.CommandText = "select *from Nation where NationCode = @a";
                cmd.Parameters.Clear();
                cmd.Parameters.Add("@a", _Nation);
                conn.Open();
                SqlDataReader dr = cmd.ExecuteReader();
                if (dr.HasRows)
                {
                    dr.Read();
                    end = dr["NationName"].ToString();
                }
                conn.Close();

                return end;
            }
        }