读取数据库的数据并转换成List<>

一、在有帮助类DbHelperSQL的时候

1、下为其中返回SqlDataReader的方法

/// <summary>
        /// 执行查询语句，返回SqlDataReader ( 注意：调用该方法后，一定要对SqlDataReader进行Close )
        /// </summary>
        /// <param name="strSQL">查询语句</param>
        /// <returns>SqlDataReader</returns>
        public static SqlDataReader ExecuteReader(string strSQL)
        {
            SqlConnection connection = new SqlConnection(connectionString);
            SqlCommand cmd = new SqlCommand(strSQL, connection);
            try
            {
                connection.Open();
                SqlDataReader myReader = cmd.ExecuteReader(CommandBehavior.CloseConnection);
                return myReader;
            }
            catch (System.Data.SqlClient.SqlException e)
            {
                throw e;
            }   

        }

2、三层DAL层方法

/// <summary>
        /// 把读出的数据转换成List
        /// </summary>
        public List<int> GetUserList(int hid)
        {
            string sql = " select V_UserID from UserVoters where V_HeadlineID=" + hid + "";
            SqlDataReader dr = DbHelperSQL.ExecuteReader(sql);
            List<UserVotersModel> plist = new List<UserVotersModel>();
            while (dr.Read())
            {
                UserVotersModel uvm = new UserVotersModel();
                uvm.V_UserID = int.Parse(dr["V_UserID"].ToString());
                plist.Add(uvm);
            }
            List<int> list = new List<int>();
            for (int i = 0; i < plist.Count; i++)
            {
                list.Add(int.Parse(plist[i].V_UserID.ToString()));
            }
            return list;
        }

3、把List当参数放到sql语句里的方法

 /// <summary>
        /// 获得未投票用户列表
        /// </summary>
        public DataSet GetNoPersonList(List<int> list)
        {
            StringBuilder strSql = new StringBuilder();
            if (list != null && list.Count > 0)
            {
                string listMes = string.Empty;
                foreach (int str in list)
                {
                    listMes += "'" + str + "',";
                }
                strSql.Append("select U_Uid,U_Name,U_Sex,U_Phone,U_QQ  from dbo.UsersInfo where U_ID not in(" + listMes.TrimEnd(',') + ") and U_Level=4 and U_Name='' ORDER BY  U_ID DESC ");
                return DbHelperSQL.Query(strSql.ToString());
            }
            else
            {
                strSql.Append(" select U_Uid,U_Name,U_Sex,U_Phone,U_QQ  from dbo.UsersInfo where U_Level=4 and  U_Name='' ORDER BY  U_ID DESC ");
                return DbHelperSQL.Query(strSql.ToString());
            }
        }

二、没有帮助类直接读取数据库

/// <summary>
        /// 读取数据库的信息,并转换成List
        /// </summary>
        public List<MailData> GetExpiredLicense()
        {
            string connectionString = "Data Source=01;Initial Catalog=Music;Persist Security Info=True;User ID=Musicname;Password=123456";
            SqlConnection conn = new SqlConnection(connectionString);
            conn.Open();         
            string sql = string.Format( @" select * from Tale" );
            
            SqlDataAdapter da = new SqlDataAdapter(sql, connectionString);
            DataSet ds = new DataSet();
            da.Fill(ds);
            List<MailData> list = new List<MailData>(); //MailData为要查询表的实体类    
            foreach (DataRow item in ds.Tables[0].Rows)
            {
                list.Add(MailData.ConvertRow(item));
            }
            return list;
        }