知识大全创建一个三层的数据库应用程序

Posted 2022-07-17 数据库

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概论本文将介绍如何创建一个三层应用程序并且将介绍如何创建一个Web Service服务 ADO NET创建Windows三层结构应用程序的体系架构如下图所示该结构分三个层次表示层业务层数据层数据层代表物理数据库业务层负责数据层与表示层之间的数据传输表示层应用程序的客户端它通过业务层来访问数据库表示层所操作的是驻留在内存中的本地数据当需要更新数据库数据时要通过业务层提供的更新方法实现这样可以大大提高应用程序的性能而且什么时候更新数据完全由你决定提高了编程的灵活性 实例: 这里我们具体做一个实例来看看如何用VB NET创建三层结构的应用程序数据库我们选择SQL SERVER 的NorthWind数据库业务层我们创建一个WebService作为中间层（需要安装IIS服务）表示层我们写一个Windows Form 第一步创建WebService 具体步骤如下新建一个项目选择ASP NET Web服务命名为 WebService For 业务层添加两个Sql DataAdapter 一个为Customer_da 它指向NorthWind数据库的Customers表另一个为Order_da 指向Northwind数据库的Orders表然后生成一个Typed DataSet（选择数据菜单的生成数据集）命名为 Super_ds 数据库连接已经完成下一步我们将考虑它与表示层之间的通信这里我们定义两个方法一个为 Get_DataSet 它返回一个Super_ds类型的数据集另一个为 Update_DataSet 它负责更新数据库数据方法代码如下 <WebMethod()> Public Function Get_Dataset() As super_ds customer_da Fill(Super_ds Customers) order_da Fill(Super_ds Orders) Return Super_ds End Function <WebMethod()> Public Sub Update_Dataset() Super_ds AcceptChanges() End Sub 你可以运行测试一下你建立的这个WebService 它将提供两个方法返回的DataSet是以XML表示的业务层的完整代码如下 Imports System Web Services Public Class Service Inherits System Web Services WebService Web Services Designer Generated Code…… <WebMethod()> Public Function Get_Dataset() As super_ds customer_da Fill(Super_ds Customers) order_da Fill(Super_ds Orders) Return Super_ds End Function <WebMethod()> Public Sub Update_Dataset() Super_ds AcceptChanges() End Sub WEB SERVICE EXAMPLE The HelloWorld() example service returns the string Hello World To build unment the following lines then save and build the project To test this web service ensure that the asmx file is the start page and press F <WebMethod()> Public Function HelloWorld() As String HelloWorld = Hello World End Function End Class 第二步创建表示层具体步骤如下新建一个Windows应用程序命名为 Windows Form For 表示层在窗体上添加一个DataGrid 一个Button Button 的text为 Load 作用是从业务层读取数据在解决方案窗体中添加Web 引用将我们自己建立的Web Service for 业务层引入到当前项目中向Button 的Click事件添加如下代码 Dim Customer_Ds As New localhost super_ds() Dim ser As New localhost Service () Customer_Ds Merge(ser Get_Dataset) DataGrid DataSource = Customer_Ds 这里我们调用了Web Service的Get_DataSet函数 Update_DataSet方法的调用与此完全相同表示层的完整代码如下 Imports Data_Access_表示层 Public Class Form Inherits System Windows Forms Form #Region Windows Form Designer generated code Public Sub New() MyBase New() This call is required by the Windows Form Designer InitializeComponent() Add any initialization after the InitializeComponent() call End Sub Form overrides dispose to clean up the ponent list Protected Overloads Overrides Sub Dispose(ByVal disposing As Boolean) If disposing Then If Not (ponents Is Nothing) Then ponents Dispose() End If End If MyBase Dispose(disposing) End Sub Friend WithEvents Button As System Windows Forms Button Friend WithEvents Button As System Windows Forms Button Friend WithEvents Button As System Windows Forms Button Friend WithEvents Client_DataSet As Data_Access_表示层 localhost super_ds Friend WithEvents DataGrid As System Windows Forms DataGrid Required by the Windows Form Designer Private ponents As System ComponentModel Container NOTE: The following procedure is required by the Windows Form Designer It can be modified using the Windows Form Designer Do not modify it using the code editor <System Diagnostics DebuggerStepThrough()> Private Sub InitializeComponent() Me Button = New System Windows Forms Button() Me Button = New System Windows Forms Button() Me Button = New System Windows Forms Button() Me Client_DataSet = New Data_Access_表示层 localhost super_ds() Me DataGrid = New System Windows Forms DataGrid() CType(Me Client_DataSet System ComponentModel ISupportInitialize) BeginInit() CType(Me DataGrid System ComponentModel ISupportInitialize) BeginInit() Me SuspendLayout() Button Me Button Location = New System Drawing Point( ) Me Button Name = Button Me Button TabIndex = Me Button Text = load Button Me Button Location = New System Drawing Point( ) Me Button Name = Button Me Button TabIndex = Me Button Text = update Button Me Button Location = New System Drawing Point( ) Me Button Name = Button Me Button TabIndex = Me Button Text = clear Client_DataSet Me Client_DataSet DataSetName = Client_DataSet Me Client_DataSet Locale = New System Globalization CultureInfo( zh CN ) Me Client_DataSet Namespace = DataGrid Me DataGrid DataMember = Me DataGrid Location = New System Drawing Point( ) Me DataGrid Name = DataGrid Me DataGrid Size = New System Drawing Size( ) Me DataGrid TabIndex = Form Me AutoScaleBaseSize = New System Drawing Size( ) Me ClientSize = New System Drawing Size( ) Me Controls AddRange(New System Windows Forms Control() Me DataGrid Me Button Me Button Me Button ) Me Name = Form Me Text = Form CType(Me Client_DataSet System ComponentModel ISupportInitialize) EndInit() CType(Me DataGrid System ComponentModel ISupportInitialize) EndInit() Me ResumeLayout(False) End Sub #End Region Private Sub Button _Click(ByVal sender As System Object ByVal e As System EventArgs) Handles Button Click Dim Customer_Ds As New localhost super_ds() Dim ser As New localhost Service () Customer_Ds Merge(ser Get_Dataset) DataGrid DataSource = Customer_Ds End Sub End Class 总结可见表示层窗体上完全没有数据库连接控件它与数据库的连接任务是通过业务层来完成的这样程序的结构更加清晰当然业务层的实现也可以用其他方法比如写一个自己的类来完成与数据库的数据传输 cha138/Article/program/net/201311/13657

知识大全 创建一个三层的数据库应用程序

知识大全创建一个三层的数据库应用程序