浅析C#中三层架构的实现

本文讨论如何在C＃中实现三层架构，使用MS Access数据库存储数据。同时在三层架构中实现一个小型的可复用的组件来保存客户数据，并提供添加、更新、查找客户数据的功能。

这篇文章讨论如何在C＃中实现三层架构，使用MS Access数据库存储数据。在此，我在3层架构中实现一个小型的可复用的组件保存客户数据。并提供添加，更新，查找客户数据的功能。

背景

首先，我介绍一些3层架构的理论知识。简单说明：什么是3层架构？3层架构的优点是什么？

什么是三层架构？

3层架构是一种“客户端－服务器”架构，在此架构中用户接口，商业逻辑，数据保存以及数据访问被设计为独立的模块。主要有3个层面，第一层（表现层，GUI层），第二层（商业对象，商业逻辑层），第三层（数据访问层）。这些层可以单独开发，单独测试。

为什么要把程序代码分为3层。把用户接口层，商业逻辑层，数据访问层分离有许多的优点。

在快速开发中重用商业逻辑组件，我们已经在系统中实现添加，更新，删除，查找客户数据的组件。这个组件已经开发并且测试通过，我们可以在其他要保存客户数据的项目中使用这个组件。

系统比较容易迁移，商业逻辑层与数据访问层是分离的，修改数据访问层不会影响到商业逻辑层。系统如果从用SQL Server存储数据迁移到用Oracle存储数据，并不需要修改商业逻辑层组件和GUI组件

系统容易修改，假如在商业层有一个小小的修改，我们不需要在用户的机器上重装整个系统。我们只需要更新商业逻辑组件就可以了。

应用程序开发人员可以并行，独立的开发单独的层。

代码

这 个组件有3层，第一个层或者称为GUI层用form实现，叫做FrmGUI。第二层或者称为商业逻辑层，叫做BOCustomer，是Bussniess Object Customer的缩写。最后是第三层或者称为数据层，叫做DACustomer，是Data Access Customer的缩写。为了方便，我把三个层编译到一个项目中。

用户接口层

下面是用户接口成的一段代码，我只选取了调用商业逻辑层的一部分代码。

//This function get the details from the user via GUI

//tier and calls the Add method of business logic layer.

private void cmdAdd_Click(object sender, System.EventArgs e)

{

try

{

cus = new BOCustomer();

cus.cusID=txtID.Text.ToString();

cus.LName = txtLName.Text.ToString();

cus.FName = txtFName.Text.ToString();

cus.Tel= txtTel.Text.ToString();

cus.Address = txtAddress.Text.ToString();

cus.Add();

}

catch(Exception err)

{

MessageBox.Show(err.Message.ToString());

}

}
 
//This function gets the ID from the user and finds the

//customer details and return the details in the form of

//a dataset via busniss object layer. Then it loops through

//the content of the dataset and fills the controls.
 
private void cmdFind_Click(object sender, System.EventArgs e)

{

try

{

String cusID = txtID.Text.ToString();
 
BOCustomer thisCus = new BOCustomer();
 
DataSet ds = thisCus.Find(cusID);
 
DataRow row;

row = ds.Tables[0].Rows[0];
 
//via looping

foreach(DataRow rows in ds.Tables[0].Rows )

{

txtFName.Text = rows["CUS_F_NAME"].ToString();

txtLName.Text = rows["CUS_L_NAME"].ToString();

txtAddress.Text = rows["CUS_ADDRESS"].ToString();

txtTel.Text = rows["CUS_TEL"].ToString();

}

}

catch (Exception err)

{

MessageBox.Show(err.Message.ToString());

}
 
}
 
//this function used to update the customer details.

private void cmdUpdate_Click(object sender, System.EventArgs e)

{

try

{

cus = new BOCustomer();

cus.cusID=txtID.Text.ToString();

cus.LName = txtLName.Text.ToString();

cus.FName = txtFName.Text.ToString();

cus.Tel= txtTel.Text.ToString();

cus.Address = txtAddress.Text.ToString();
 
cus.Update();

}

catch(Exception err)

{

MessageBox.Show(err.Message.ToString());

}

}

商业逻辑层

下面是商业逻辑层的所有代码，主要包括定义customer对象的属性。但这仅仅是个虚构的customer对象，如果需要可以加入其他的属性。商业逻辑层还包括添加，更新，查找，等方法。

商业逻辑层是一个中间层，处于GUI层和数据访问层中间。他有一个指向数据访问层的引用cusData = new DACustomer().而且还引用了System.Data名字空间。商业逻辑层使用DataSet返回数据给GUI层。

 

 

using System;

using System.Data;

namespace _3tierarchitecture

{

／／／

／／／ Summary description for BOCustomer.

／／／

public class BOCustomer

{

／／Customer properties

private String fName;

private String lName;

private String cusId;

private String address;

private String tel;

private DACustomer cusData;

public BOCustomer()

{

／／An instance of the Data access layer!

cusData = new DACustomer();

}

／／／

／／／ Property FirstName (String)

／／／

public String FName

{

get

{

return this.fName;

}

set

{

try

{

this.fName = value;

if (this.fName == "")

{

throw new Exception(

"Please provide first name ...");

}

}

catch(Exception e)

{

throw new Exception(e.Message.ToString());

}

}

}

／／／

／／／ Property LastName (String)

／／／

public String LName

{

get

{

return this.lName;

}

set

{

／／could be more checkings here eg revmove ' chars

／／change to proper case

／／blah blah

this.lName = value;

if (this.LName == "")

{

throw new Exception("Please provide name ...");

}

}

}

／／／

／／／ Property Customer ID (String)

／／／

public String cusID

{

get

{

return this.cusId;

}

set

{

this.cusId = value;

if (this.cusID == "")

{

throw new Exception("Please provide ID ...");

}

}

}

／／／

／／／ Property Address (String)

／／／

public String Address

{

get

{

return this.address;

}

set

{

this.address = value;

if (this.Address == "")

{

throw new Exception("Please provide address ...");

}

}

}

／／／

／／／ Property Telephone (String)

／／／

public String Tel

{

get

{

return this.tel;

}

set

{

this.tel = value;

if (this.Tel == "")

{

throw new Exception("Please provide Tel ...");

}

}

}

／／／

／／／ Function Add new customer. Calls

／／／ the function in Data layer.

／／／

public void Add()

{

cusData.Add(this);

}

／／／

／／／ Function Update customer details.

／／／ Calls the function in Data layer.

／／／

public void Update()

{

cusData.Update(this);

}

／／／

／／／ Function Find customer. Calls the

／／／ function in Data layer.

／／／ It returns the details of the customer using

／／／ customer ID via a Dataset to GUI tier.

／／／

public DataSet Find(String str)

{

if (str == "")

throw new Exception("Please provide ID to search");

DataSet data = null;

data = cusData.Find(str);

return data;

}

}

}

 

数据访问层

数据层包括处理MS Access数据库的细节。所有这些细节都是透明的，不会影响到商业逻辑层。数据访问层有个指向商业逻辑层的引用BOCustomer cus。为了应用方便并且支持其他数据库。

 

using System;

using System.Data.OleDb;

using System.Data;

namespace _3tierarchitecture

{

///

/// Summary description for DACustomer.

///

public class DACustomer

{

private OleDbConnection cnn;

//change connection string as per the

//folder you unzip the files

private const string CnnStr =

"Provider=Microsoft.Jet.OLEDB.4.0;Data " +

"Source= D:\\Rahman_Backup\\Programming\\" +

"Csharp\\3tierarchitecture\\customer.mdb;";

//local variables

private String strTable="";

private String strFields="";

private String strValues="";

private String insertStr="";

//this needs to be changed based on customer

//table fields' Name of the database!

private const String thisTable = "tblCustomer";

private const String cus_ID = "CUS_ID";

private const String cus_LName = "CUS_L_NAME";

private const String cus_FName = "CUS_F_NAME";

private const String cus_Tel = "CUS_TEL";

private const String cus_Address = "CUS_ADDRESS";

public DACustomer()

{

}

public DACustomer(BOCustomer cus)

{

// A reference of the business object class

}

//standard dataset function that adds a new customer

public void Add(BOCustomer cus)

{

String str = BuildAddString(cus);

OpenCnn();

//Open command option - cnn parameter is imporant

OleDbCommand cmd = new OleDbCommand(str,cnn);

//execute connection

cmd.ExecuteNonQuery();

// close connection

CloseCnn();

}

//standard dataset function that updates

//details of a customer based on ID

public void Update(BOCustomer cus)

{

OpenCnn();

String selectStr = "UPDATE " + thisTable +

" set " + cus_LName + " = '" + cus.LName + "'" +

", " + cus_FName + " = '" + cus.FName + "'" +

", " + cus_Address + " = '" + cus.Address + "'" +

", " + cus_Tel + " = '" + cus.Tel + "'" +

" where cus_ID = '" + cus.cusID + "'";

OleDbCommand cmd = new OleDbCommand(selectStr,cnn);

cmd.ExecuteNonQuery();

CloseCnn();

}

//standard dataset function that finds and

//return the detail of a customer in a dataset

public DataSet Find(String argStr)

{

DataSet ds=null;

try

{

OpenCnn();

String selectStr = "select * from " + thisTable +

" where cus_ID = '" + argStr + "'";

OleDbDataAdapter da =

new OleDbDataAdapter(selectStr,cnn);

ds = new DataSet();

da.Fill(ds,thisTable);

CloseCnn();

}

catch(Exception e)

{

String Str = e.Message;

}

return ds;

}

private void OpenCnn()

{

// initialise connection

String cnnStr = CnnStr;

cnn = new OleDbConnection(cnnStr);

// open connection

cnn.Open();

}

private void CloseCnn()

{

// 5- step five

cnn.Close();

}

// just a supporting function that builds

// and return the insert string for dataset.

private String BuildAddString(BOCustomer cus)

{

// these are the constants as

// set in the top of this module.

strTable="Insert into " + thisTable;

strFields=" (" + cus_ID +

"," + cus_LName +

"," + cus_FName +

"," + cus_Address +

"," + cus_Tel + ")";

//these are the attributes of the

//customer business object.

strValues= " Values ( '" + cus.cusID +

"' , '" + cus.LName +

"' , '" + cus.FName +

"' , '" + cus.Address +

"' , '" + cus.Tel + "' )";

insertStr = strTable + strFields + strValues;

return insertStr;

}

}

}