C#_数据访问类查询 和 属性扩展

 public class Users
    {
        private string _UserName;

        /// <summary>
        /// 用户名
        /// </summary>
        public string UserName
        {
            get { return _UserName; }
            set { _UserName = value; }
        }
        private string _PassWord;

        /// <summary>
        /// 密码
        /// </summary>
        public string PassWord
        {
            get { return _PassWord; }
            set { _PassWord = value; }
        }
        private string _NickName;

        /// <summary>
        /// 昵称
        /// </summary>
        public string NickName
        {
            get { return _NickName; }
            set { _NickName = value; }
        }


        private bool _Sex;

        /// <summary>
        /// 性别
        /// </summary>
        public bool Sex
        {
            get { return _Sex; }
            set { _Sex = value; }
        }

        public string SexStr
        {
            get { return _Sex ? "男" : "女"; }
        }
        private DateTime _Birthday;
        /// <summary>
        /// 生日
        /// </summary>
        public DateTime Birthday
        {
            get { return _Birthday; }
            set { _Birthday = value; }
        }

        public string BirthdayStr
        {
            get { return _Birthday.ToString("yyyy年MM月dd日"); }
        }
        private string _Nation;

        /// <summary>
        /// 民族
        /// </summary>
        public string Nation
        {
            get { return _Nation; }
            set { _Nation = value; }
        }

        public string NationName
        {
            get
            {
                NationData Ndata = new NationData();
                string end = Ndata.Select(_Nation);
                return end;
            }
        }

public List<Users> Select()
        {
            //泛型集合，放置所有Users数据对象
            List<Users> list = new List<Users>();

            cmd.CommandText = "select *from Users";

            conn.Open();
            SqlDataReader dr = cmd.ExecuteReader();
            if (dr.HasRows)//如果数据表中有数据
            {
                while (dr.Read())//循环读取全部数据
                {
                    //没读取一行数据，就制作一个Users对象
                    Users u = new Users();
                    u.UserName = dr["UserName"].ToString();
                    u.PassWord = dr["PassWord"].ToString();
                    u.NickName = dr["NickName"].ToString();
                    u.Sex = Convert.ToBoolean(dr["Sex"]);
                    u.Birthday = Convert.ToDateTime(dr["Birthday"]);
                    u.Nation = dr["Nation"].ToString();

                    //注意，在循环中，将制作好的每一个对象，都放到集合中去
                    list.Add(u);
                }
            }
            conn.Close();
            return list;
        }

 public class NationData
    {
        SqlConnection conn = null;
        SqlCommand cmd = null;

        public NationData()
        {
            conn = new SqlConnection("server=.;database=Data0720;user=sa;pwd=123");
            cmd = conn.CreateCommand();
        }

        public string Select(string code)
        {
            string end = "<无>";

            cmd.CommandText = "select *from Nation where NationCode=@a";
            cmd.Parameters.Clear();
            cmd.Parameters.Add("@a", code);

            conn.Open();
            SqlDataReader dr = cmd.ExecuteReader();
            if (dr.HasRows)
            {
                dr.Read();
                end = dr["NationName"].ToString();
            }

            conn.Close();
            return end;
        }

 public class Nation
    {
        private string _NationCode;

        public string NationCode
        {
            get { return _NationCode; }
            set { _NationCode = value; }
        }

        private string _NationName;

        public string NationName
        {
            get { return _NationName; }
            set { _NationName = value; }
        }

    }