.net三层结构初探分析-程序员之家

对于学习，我选择了ACCESS数据库+存储过程的方式，这里记录的是我个人的学习体会和笔记，与网上的可能有不同之处，观点也不可能全部相同。
为什么使用三层结构：
首先要明确，三层结构并不能使系统变快，实际上它会比起“单类结构”慢。但越来越多人使用三层结构开发，为啥呢？我在使用中，发现三层结构十分清晰，一个类，一个文件你该放在哪层就放哪层，不会象单类结构那样全部放到App_Data中，造成结构混乱。当然，使用三层结构的原因肯定不是那么肤浅，它对团队开发，系统可维护性有十分重要的意义。

三层结构是代码量增多，且代码多重复？
确实，三层代码要写很多很白痴，很简单的代码，比如MODEL这个实体类，如果你需要一个admin的实体，那么你需要写这样的代码：

实现代码如下：

public class admin 
{ 
private int? _id; 
private string _sname; 
private string _spassword; 

public int? id 
{ 
set { _id = value; } 
get { return _id; } 
} 

public string sname 
{ 
set { _sname = value; } 
get { return _sname; } 
} 

public string spassword 
{ 
set { _spassword = value; } 
get { return _spassword; } 
} 
} 

而有多个实体的话，你要再写这些白痴代码，为什么叫它白痴代码？因为这些代码你看着个表就可以写出来了。一次和老汤讨论中，介绍了一个软件，叫做“动软.Net代码生成器”，这些白痴代码让这个软件自己去生成吧！在这里也推荐大家用这个软件，可以减少很多代码量，BLL,DAL,WEB层的代码都可以去生成，但要完全符合使用的话，还需要自己做些修改。

下面讲讲我理解的三层，先上张图1：

WEB ：界面层，其实就是一个网站。
BLL：逻辑处理层。
DAL：数据访问层
DBUtility：数据层基类
Model：实体类
Common：存放公用函数

图2

这里需要讲讲那个DBUtility这个层，你可以看到有4个文件：
1、DbHelperOleDb.cs：用于SQL语句
2、DbHelperOleDbP.cs：用于存储过程
3、DbHelperOleDbS.cs：用于具体实现，比如“根据条件判断是否存在”、“返回最大的ID”...
4、PubConstant.cs：数据库连接代码

三层结构要求不能跨层访问，在图1中大家可以看到，3个层之间是逐层依赖的。与普通“单类结构”最明显的区别是，这里举一个添加数据的例子(伪代码)：

单类结构(直接依赖于数据基类)：

string sname = "阿会楠";
string surl = "sosuo8.com";
string strSql = "insert into admin(sname,surl) values('" + sname + "','" + surl + ')";
DB.exeSQL(strSql);

我想对于单类结构来说，总是在WEB层拼凑SQL语句，然后调用数据操作类执行SQL语句，这样速度确实快一些。

看看三层结构：
web层：

string sname = "阿会楠";
string surl = "sosuo8.com";
Model.admin model = new Model.admin();//实体类
model.sname = sname;
mode.surl = surl:
BLL.admin bll = new BLL.admin();
bll.Add(model);

BLL层：

public void Add(MODEL.admin model)
{
dal.Add(model);
}

DAL层（需要依赖于DBUtility数据基类）：

public void Add(Model.admin model)
{
string strSql = "insert into admin(sname,surl) values('" + model.sname + "','" + model.surl + "')":
DB.executeSQL(strSql);
}

Model实体类：

private string _sname;
private string _surl:
public string sname
{
       set{_sname = value;}
       get{return _sname};
}
public string surl
{
       set{_surl = value;}
       get{return _surl;}
}

你看出之间一层层的依赖关系了吗？“单类结构”直接就是WEB->DBUtility，而三层是WEB->BLL->DAL->DBUtility，MODEL作为实体类都可以不算一个层，COMMON也是，DBUtlity也是，它们只能算是把具有共同使用功能的代码堆放在一起。所以，三层就是WEB(界面层)->BLL(逻辑处理层)->DAL(数据访问层)，并且是层层依赖。而后面引申出来的项目（COMMON,MODEL,DBUtlity），并不算层。按我理解是这样，如果有什么理解错误或不妥的地方欢迎指出，大家一起讨论。

最好的学习方法就是看代码，我写了比较简单的给大家学习下：

下面贴出相关代码：
web.config
<appSettings>
<add key="ConnectionString" value="Provider=Microsoft.Jet.OleDb.4.0;Data Source=|DataDirectory|data.mdb" />
</appSettings>
DBUtility--PubConstant.cs(连接字符串)

实现代码如下：

using System; 
using System.Configuration; 

namespace MyCms.DBUtility 
{ 
public class PubConstant 
{ 
public static string ConnectionString 
{ 
get 
{ 
return ConfigurationSettings.AppSettings["ConnectionString"]; 
} 
} 
} 
}

DBUtility--DbHelperOleDb.cs(数据基类SQL语句)

实现代码如下：

using System; 
using System.Collections; 
using System.Text; 
using System.Data; 
using System.Data.OleDb; 

namespace MyCms.DBUtility 
{ 
//数据访问基类(基于OleDb) 
public partial class DbHelperOleDb 
{ 
//数据库连接字符串，在web.config中配置 
public static string ConnectionString = PubConstant.ConnectionString; 
public DbHelperOleDb() 
{ 
} 

/// <summary> 
/// 执行SQL语句，返回影响的记录数 
/// </summary> 
/// <param name="strSql">SQL语句</param> 
/// <returns>影响的记录数</returns> 
public static int ExecuteSql(string strSql) 
{ 
using (OleDbConnection conn = new OleDbConnection(ConnectionString)) 
{ 
using (OleDbCommand cmd = new OleDbCommand(strSql, conn)) 
{ 
try 
{ 
conn.Open(); 
return cmd.ExecuteNonQuery(); 
} 
catch(OleDbException E) 
{ 
conn.Close(); 
throw new Exception(E.Message); 
} 

} 
} 
} 

/// <summary> 
/// 执行多条SQL语句，实现数据库事务 
/// </summary> 
/// <param name="SqlStrList">多条SQL语句</param> 
public static void ExecuteSqlTran(ArrayList SqlStrList) 
{ 
using (OleDbConnection conn = new OleDbConnection(ConnectionString)) 
{ 
conn.Open(); 
OleDbCommand cmd = new OleDbCommand(); 
cmd.Connection = conn; 
OleDbTransaction tx = conn.BeginTransaction(); 
cmd.Transaction = tx; 
try 
{ 
for (int n = 0; n < SqlStrList.Count; n++) 
{ 
string strSql = SqlStrList[n].ToString(); 
if (strSql.Trim().Length > 1) 
{ 
cmd.CommandText = strSql; 
cmd.ExecuteNonQuery(); 
} 
} 
tx.Commit(); 
} 
catch (System.Data.OleDb.OleDbException E) 
{ 
tx.Rollback(); 
throw new Exception(E.Message); 
} 
} 
} 

/// <summary> 
/// 执行带一个存储过程参数的SQL语句 
/// </summary> 
/// <param name="strSql">SQL语句</param> 
/// <param name="content">参数内容，比如一个字段是格式复杂的文章</param> 
/// <returns>影响的记录数</returns> 
public static int ExecuteSinglePro(string strSql, string content) 
{ 
using (OleDbConnection conn = new OleDbConnection(ConnectionString)) 
{ 
OleDbCommand cmd = new OleDbCommand(strSql, conn); 
OleDbParameter myParameter = new OleDbParameter("@content",OleDbType.VarChar); 
myParameter.Value = content; 
cmd.Parameters.Add(myParameter); 
try 
{ 
conn.Open(); 
return cmd.ExecuteNonQuery(); 
} 
catch (OleDbException E) 
{ 
throw new Exception(E.Message); 
} 
finally 
{ 
cmd.Dispose(); 
conn.Close(); 
} 

} 
} 

/// <summary> 
/// 执行一条计算查询结果语句，返回查询结果 
/// </summary> 
/// <param name="strSql">SQL语句</param> 
/// <returns>查询结果</returns> 
public static object GetSingle(string strSql) 
{ 
using (OleDbConnection conn = new OleDbConnection(ConnectionString)) 
{ 
using (OleDbCommand cmd = new OleDbCommand(strSql, conn)) 
{ 
try 
{ 
conn.Open(); 
object obj = cmd.ExecuteScalar(); 
if ((Equals(obj, null)) || Equals(obj, DBNull.Value)) 
{ 
return null; 
} 
else 
{ 
return obj; 
} 
} 
catch (OleDbException E) 
{ 
conn.Close(); 
throw new Exception(E.Message); 
} 
} 
} 
} 

/// <summary> 
/// 返回OleDbDataReader 
/// </summary> 
/// <param name="strSql">查询语句</param> 
/// <returns>OleDbDataReader</returns> 
public static OleDbDataReader ExecuteReader(string strSql) 
{ 
OleDbDataReader dr = null; 
using (OleDbConnection conn = new OleDbConnection(ConnectionString)) 
{ 
using(OleDbCommand cmd = new OleDbCommand(strSql,conn)) 
{ 
try 
{ 
conn.Open(); 
cmd.CommandText = strSql; 
cmd.CommandType = CommandType.Text; 
dr = cmd.ExecuteReader(); 
} 
catch 
{ 
dr.Close(); 
conn.Close(); 
cmd.Dispose(); 
} 
} 
} 
return dr; 
} 

/// <summary> 
/// 执行查询语句，返回DataSet 
/// </summary> 
/// <param name="strSql">查询语句</param> 
/// <returns>DataSet</returns> 
public static DataSet Query(string strSql) 
{ 
using (OleDbConnection conn = new OleDbConnection(ConnectionString)) 
{ 
DataSet ds = new DataSet(); 
try 
{ 
conn.Close(); 
OleDbDataAdapter da = new OleDbDataAdapter(strSql, conn); 
da.Fill(ds, "ds"); 
} 
catch (OleDbException E) 
{ 
throw new Exception(E.Message); 
} 
return ds; 
} 
} 


} 
} 

DBUtility--DbHelperOleDbP.cs(数据基类存储过程)

实现代码如下：

using System; 
using System.Collections; 
using System.Collections.Generic; 
using System.Text; 
using System.Data; 
using System.Data.OleDb; 

namespace MyCms.DBUtility 
{ 
public partial class DbHelperOleDb 
{ 

/// <summary> 
/// 执行SQL语句，返回影响的记录数 
/// </summary> 
public static int ExecuteSql(string strSql, params OleDbParameter[] parms) 
{ 
using (OleDbConnection conn = new OleDbConnection(ConnectionString)) 
{ 
using (OleDbCommand cmd = new OleDbCommand()) 
{ 
try 
{ 
PrepareCmd(cmd, conn, null, strSql, parms); 
int rows = cmd.ExecuteNonQuery(); 
cmd.Parameters.Clear(); 
return rows; 
} 
catch (OleDbException E) 
{ 
throw new Exception(E.Message); 
} 
} 
} 
} 


/// <summary> 
/// 执行一条计算查询结果语句，返回查询结果（object）。 
/// </summary> 
/// <param name="SQLString">计算查询结果语句</param> 
/// <returns>查询结果（object）</returns> 
public static object GetSingle(string SQLString, params OleDbParameter[] cmdParms) 
{ 
using (OleDbConnection connection = new OleDbConnection(ConnectionString)) 
{ 
using (OleDbCommand cmd = new OleDbCommand()) 
{ 
try 
{ 
PrepareCmd(cmd, connection, null, SQLString, cmdParms); 
object obj = cmd.ExecuteScalar(); 
cmd.Parameters.Clear(); 
if ((Object.Equals(obj, null)) || (Object.Equals(obj, System.DBNull.Value))) 
{ 
return null; 
} 
else 
{ 
return obj; 
} 
} 
catch (System.Data.OleDb.OleDbException e) 
{ 
throw new Exception(e.Message); 
} 
} 
} 
} 

/// <summary> 
/// 执行查询语句，返回OleDbDataReader 
/// </summary> 
/// <param name="strSQL">查询语句</param> 
/// <returns>OleDbDataReader</returns> 
public static OleDbDataReader ExecuteReader(string SQLString, params OleDbParameter[] cmdParms) 
{ 
OleDbConnection connection = new OleDbConnection(ConnectionString); 
OleDbCommand cmd = new OleDbCommand(); 
try 
{ 
PrepareCmd(cmd, connection, null, SQLString, cmdParms); 
OleDbDataReader myReader = cmd.ExecuteReader(); 
cmd.Parameters.Clear(); 
return myReader; 
} 
catch (System.Data.OleDb.OleDbException e) 
{ 
throw new Exception(e.Message); 
} 

} 

/// <summary> 
/// 执行查询语句，返回DataSet 
/// </summary> 
/// <param name="SQLString">查询语句</param> 
/// <returns>DataSet</returns> 
public static DataSet Query(string SQLString, params OleDbParameter[] cmdParms) 
{ 
using (OleDbConnection connection = new OleDbConnection(ConnectionString)) 
{ 
OleDbCommand cmd = new OleDbCommand(); 
PrepareCmd(cmd, connection, null, SQLString, cmdParms); 
using (OleDbDataAdapter da = new OleDbDataAdapter(cmd)) 
{ 
DataSet ds = new DataSet(); 
try 
{ 
da.Fill(ds, "ds"); 
cmd.Parameters.Clear(); 
} 
catch (System.Data.OleDb.OleDbException ex) 
{ 
throw new Exception(ex.Message); 
} 
return ds; 
} 
} 
} 

///添加存储过程参数 
private static void PrepareCmd(OleDbCommand cmd, OleDbConnection conn, OleDbTransaction trans, string cmdText, OleDbParameter[] cmdParms) 
{ 
if (conn.State == ConnectionState.Closed) 
{ 
conn.Open(); 
} 
cmd.Connection = conn; 
cmd.CommandText = cmdText; 
if (trans != null) 
{ 
cmd.Transaction = trans; 
} 
cmd.CommandType = CommandType.Text; 
if (cmdParms != null) 
{ 
foreach (OleDbParameter parm in cmdParms) 
cmd.Parameters.Add(parm); 
} 
} 

/// <summary> 
/// 执行多条SQL语句，实现数据库事务。 
/// </summary> 
/// <param name="SQLStringList">SQL语句的哈希表（key为sql语句，value是该语句的OleDbParameter[]）</param> 
public static void ExecuteSqlTran(Hashtable SQLStringList) 
{ 
using (OleDbConnection conn = new OleDbConnection(ConnectionString)) 
{ 
conn.Open(); 
using (OleDbTransaction trans = conn.BeginTransaction()) 
{ 
OleDbCommand cmd = new OleDbCommand(); 
try 
{ 
//循环 
foreach (DictionaryEntry myDE in SQLStringList) 
{ 
string cmdText = myDE.Key.ToString(); 
OleDbParameter[] cmdParms = (OleDbParameter[])myDE.Value; 
PrepareCmd(cmd, conn, trans, cmdText, cmdParms); 
int val = cmd.ExecuteNonQuery(); 
cmd.Parameters.Clear(); 

trans.Commit(); 
} 
} 
catch 
{ 
trans.Rollback(); 
throw; 
} 
} 
} 
} 

} 
} 

DBUtility--DbHelperOleDbS.cs(数据基类具体实现) 折叠展开C#复制代码
using System;
using System.Data;
using System.Data.OleDb;
using System.Text;

namespace MyCms.DBUtility
{
public partial class DbHelperOleDb
{
//根据条件判断是否存在
public static bool Exists(string strSql, params OleDbParameter[] parms)
{
object obj = DbHelperOleDb.GetSingle(strSql, parms);
int result;
if ((Equals(obj, null)) || (Equals(obj, DBNull.Value)))
{
result = 0;
}
else
{
result = int.Parse(obj.ToString());
}
if (result == 0)
{
return false;
}
else
{
return true;
}
}

}
}
DAL--admin.cs 折叠展开C#复制代码
using System;
using System.Collections.Generic;
using System.Text;
using System.Data;
using System.Data.OleDb;
using MyCms.DBUtility;

namespace MyCms.DAL
{
public class admin
{
public admin()
{
}

/// <summary>
/// 是否存在该记录
/// </summary>
public bool Exists(string sname)
{
StringBuilder strSql = new StringBuilder();
strSql.Append("select count(1) from admin");
strSql.Append(" where sname = @sname");
OleDbParameter[] parameters = {
new OleDbParameter("@sname",OleDbType.VarChar,50)};
parameters[0].Value = sname;
return DbHelperOleDb.Exists(strSql.ToString(), parameters);
}

/// <summary>
/// 增加一条记录
/// </summary>
public void Add(MyCms.MODEL.admin model)
{
StringBuilder strSql = new StringBuilder();
strSql.Append("insert into admin(");
strSql.Append("sname,spassword)");
strSql.Append(" values (");
strSql.Append("@sname,@spassword)");
OleDbParameter[] parameters = {
new OleDbParameter("@sname", OleDbType.VarChar,50),
new OleDbParameter("@spassword", OleDbType.VarChar,50)};
parameters[0].Value = model.sname;
parameters[1].Value = model.spassword;

DbHelperOleDb.ExecuteSql(strSql.ToString(), parameters);
}

/// <summary>
/// 更新一条数据
/// </summary>
public void Update(MyCms.MODEL.admin model)
{
StringBuilder strSql = new StringBuilder();
strSql.Append("update admin set ");
strSql.Append("sname=@sname,");
strSql.Append("spassword=@spassword");
strSql.Append(" where sname=@sname and spassword=@spassword ");
OleDbParameter[] parameters = {
new OleDbParameter("@sname", OleDbType.VarChar,50),
new OleDbParameter("@spassword", OleDbType.VarChar,50)};
parameters[0].Value = model.sname;
parameters[1].Value = model.spassword;

DbHelperOleDb.ExecuteSql(strSql.ToString(), parameters);
}

/// <summary>
/// 删除一条数据
/// </summary>
public void Delete(int id)
{
StringBuilder strSql = new StringBuilder();
strSql.Append("delete from admin ");
strSql.Append(" where id=@id ");
OleDbParameter[] parameters = {
new OleDbParameter("@id", OleDbType.Integer,4)};
parameters[0].Value = id;

DbHelperOleDb.ExecuteSql(strSql.ToString(), parameters);
}

/// 获取数据列表
public DataSet GetList(string strWhere)
{
StringBuilder strSql = new StringBuilder();
strSql.Append("select id,sname,spassword from admin ");
if (strWhere.Trim() != "")
{
strSql.Append(" where " + strWhere);
}
return DbHelperOleDb.Query(strSql.ToString());
}
}
}
BLL--admin.cs 折叠展开C#复制代码
using System;
using System.Data;

namespace MyCms.BLL
{
public class admin
{
private readonly MyCms.DAL.admin dal = new MyCms.DAL.admin();

public admin() { }

/// <summary>
/// 是否存在该记录
/// </summary>
public bool Exists(string sname)
{
return dal.Exists(sname);
}

/// <summary>
/// 增加一条记录
/// </summary>
public void Add(MyCms.MODEL.admin model)
{
dal.Add(model);
}

/// <summary>
/// 更新一条记录
/// </summary>
public void Update(MyCms.MODEL.admin model)
{
dal.Update(model);
}

/// <summary>
/// 删除一条记录
/// </summary>
public void Delete(int id)
{
dal.Delete(id);
}

/// <summary>
/// 获取数据列表
/// </summary>

public DataSet GetList(string strWhere)
{
return dal.GetList(strWhere);
}

/// <summary>
/// 获得数据列表
/// </summary>
public DataSet GetAllList()
{
return GetList("");
}
}
}
MODEL--admin.cs 折叠展开C#复制代码
using System;
using System.Collections.Generic;
using System.Text;

namespace MyCms.MODEL
{
public class admin
{
private int? _id;
private string _sname;
private string _spassword;

public int? id
{
set { _id = value; }
get { return _id; }
}

public string sname
{
set { _sname = value; }
get { return _sname; }
}

public string spassword
{
set { _spassword = value; }
get { return _spassword; }
}
}
}
default.aspx 折叠展开XML/HTML复制代码
<%@ Page Language="C#" AutoEventWireup="true" CodeBehind="Default.aspx.cs" Inherits="WEB._Default" %>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<html xmlns="http://www.w3.org/1999/xhtml" >
<head runat="server">
<title>无标题页</title>
</head>
<body>
<form id="form1" runat="server">
<div>
<table cellSpacing="0" cellPadding="0" width="100%" border="0">
<tr>
<td height="25" width="30%" align="right">
姓名 </td>
<td height="25" width="*" align="left">
<asp:TextBox id="txtsname" runat="server" Width="200px"></asp:TextBox>
</td></tr>
<tr>
<td height="25" width="30%" align="right">
密码 </td>
<td height="25" width="*" align="left">
<asp:TextBox id="txtspassword" runat="server" Width="200px"></asp:TextBox>
</td></tr>
<tr>
<td height="25" colspan="2"><div align="center">
<asp:Button ID="btnAdd" runat="server" Text="· 提交 ·" OnClick="btnAdd_Click" />
</div></td></tr>
</table>
</div>
<br />
数据显示：
<asp:Repeater ID="rptAdmin" runat="server">
<HeaderTemplate>
<table border="1">
<tr><th>ID</th><th>帐户</th><th>密码</th></tr>
</HeaderTemplate>
<ItemTemplate>
<tr>
<td><%#Eval("id") %></td>
<td><%#Eval("sname") %></td>
<td><%#Eval("spassword") %></td>
</tr>
</ItemTemplate>
<FooterTemplate>
</table>
</FooterTemplate>
</asp:Repeater>
</form>
</body>
</html>
default.aspx.cs 折叠展开C#复制代码
using System;
using System.Data;
using System.Configuration;
using System.Collections;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using MyCms.BLL;
using MyCms.MODEL;

///阿会楠的练习 sosuo8.com
namespace WEB
{
public partial class _Default : System.Web.UI.Page
{
protected void Page_Load(object sender, EventArgs e)
{
bind();
}

/// 添加记录
protected void btnAdd_Click(object sender, EventArgs e)
{
string sname = this.txtsname.Text;
string spassword = this.txtspassword.Text;
MyCms.MODEL.admin model = new MyCms.MODEL.admin();
model.sname = sname;
model.spassword = spassword;
MyCms.BLL.admin bll = new MyCms.BLL.admin();
bll.Add(model);
bind();
}

/// 绑定数据
protected void bind()
{
MyCms.BLL.admin admin = new MyCms.BLL.admin();
this.rptAdmin.DataSource = admin.GetAllList();
this.rptAdmin.DataBind();
}
}
}
注明：大部分代码都来自“动软.Net代码生成器”

net_sancen.rar

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