| 这篇文章讨论如何在c＃中实现3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3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> /// Summary description for BOCustomer. /// </SUMMARY> 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(); } /// <SUMMARY> /// Property FirstName (String) /// </SUMMARY> 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()); } } } /// <SUMMARY> /// Property LastName (String) /// </SUMMARY> 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 ..."); } } } /// <SUMMARY> /// Property Customer ID (String) /// </SUMMARY> public String cusID { get { return this.cusId; } set { this.cusId = value; if (this.cusID == "") { throw new Exception("Please provide ID ..."); } } } /// <SUMMARY> /// Property Address (String) /// </SUMMARY> public String Address { get { return this.address; } set { this.address = value; if (this.Address == "") { throw new Exception("Please provide address ..."); } } } /// <SUMMARY> /// Property Telephone (String) /// </SUMMARY> public String Tel { get { return this.tel; } set { this.tel = value; if (this.Tel == "") { throw new Exception("Please provide Tel ..."); } } } /// <SUMMARY> /// Function Add new customer. Calls /// the function in Data layer. /// </SUMMARY> public void Add() { cusData.Add(this); } /// <SUMMARY> /// Function Update customer details. /// Calls the function in Data layer. /// </SUMMARY> public void Update() { cusData.Update(this); } /// <SUMMARY> /// 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. /// </SUMMARY> 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> /// Summary description for DACustomer. /// </SUMMARY> 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; } } } |
