初学三层结构问题

namespace CodematicDemo.DAL.Folder

{

/// <summary>

/// 数据访问类cdcurr。

/// </summary>

public class cdcurr

{

public cdcurr()

{}

#region 成员方法

/// <summary>

/// 得到最大ID

/// </summary>

public int GetMaxId()

{

return DbHelperSQL.GetMaxID("curr", "cdcurr");

}

/// <summary>

/// 是否存在该记录

/// </summary>

public bool Exists(string curr)

{

StringBuilder strSql=new StringBuilder();

strSql.Append("select count(1) from cdcurr where curr=""+curr+""");

return DbHelperSQL.Exists(strSql.ToString());

}

/// <summary>

/// 增加一条数据

/// </summary>

public string Add(CodematicDemo.Model.Folder.cdcurr model)

{

//model.curr=GetMaxId();

StringBuilder strSql=new StringBuilder();