数据访问类查询.

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

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

        /// <summary>
        /// Users表添加方法
        /// </summary>
        /// <param name="u">要添加到数据库的Users对象</param>
        public void Insert(Users u)
        {
            cmd.CommandText = "insert into Users values(@a,@b,@c,@d,@e,@f)";
            cmd.Parameters.Clear();
            cmd.Parameters.Add("@a", u.UserName);
            cmd.Parameters.Add("@b", u.PassWord);
            cmd.Parameters.Add("@c", u.NickName);
            cmd.Parameters.Add("@d", u.Sex);
            cmd.Parameters.Add("@e", u.Birthday);
            cmd.Parameters.Add("@f", u.Nation);

            conn.Open();
            cmd.ExecuteNonQuery();
            conn.Close();
        }

        public Users Select(string Uname)
        {
            Users u = null;

            cmd.CommandText = "select *from Users where UserName=@a";
            cmd.Parameters.Clear();
            cmd.Parameters.Add("@a", Uname);

            conn.Open();
            SqlDataReader dr = cmd.ExecuteReader();
            if (dr.HasRows)
            {
                dr.Read();
                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();
            }
            conn.Close();
            return u;
        }

        public bool Delete(string Uname)
        {
            bool delOK = false;

            cmd.CommandText = "delete from Users where UserName =@a";
            cmd.Parameters.Clear();
            cmd.Parameters.Add("@a", Uname);
            conn.Open();
            try
            {
                cmd.ExecuteNonQuery();
                delOK = true;
            }
            catch { }

            conn.Close();

            return delOK;

        }

        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 void Select1()
        {
            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
                {
                    Console.WriteLine(dr["UserName"] + "  " + dr["PassWord"]);
                }
            }
            conn.Close();
        }
    }
}