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用VB.Net創建一個三層的數據庫應用程序

2013-11-13 10:21:38  來源: .NET編程 

   概論

  本文將介紹如何創建一個三層應用程序並且將介紹如何創建一個Web Service服務

  ADONET創建Windows三層結構應用程序的體系架構如下圖所示

  該結構分三個層次表示層業務層數據層

  數據層代表物理數據庫

  業務層負責數據層與表示層之間的數據傳輸

  表示層應用程序的客戶端它通過業務層來訪問數據庫

  表示層所操作的是駐留在內存中的本地數據當需要更新數據庫數據時要通過業務層提供的更新方法實現這樣可以大大提高應用程序的性能而且什麼時候更新數據完全由你決定提高了編程的靈活性

  實例

  這裡我們具體做一個實例來看看如何用VBNET創建三層結構的應用程序

  數據庫我們選擇SQL SERVER 的NorthWind數據庫

  業務層我們創建一個WebService作為中間層(需要安裝IIS服務)

  表示層我們寫一個Windows Form

  第一步創建WebService

  具體步驟如下

   新建一個項目選擇ASPNET Web服務命名為WebService For 業務層

   添加兩個Sql DataAdapter一個為Customer_da它指向NorthWind數據庫的Customers表另一個為Order_da指向Northwind數據庫的Orders表

   然後生成一個Typed DataSet(選擇數據菜單的生成數據集命名為Super_ds

   數據庫連接已經完成下一步我們將考慮它與表示層之間的通信這裡我們定義兩個方法一個為Get_DataSet它返回一個Super_ds類型的數據集另一個為Update_DataSet它負責更新數據庫數據 方法代碼如下

  <WebMethod()> Public Function Get_Dataset() As super_ds

  customer_daFill(Super_dsCustomers)

  order_daFill(Super_dsOrders)

  Return Super_ds

  End Function

  <WebMethod()> Public Sub Update_Dataset()

  Super_dsAcceptChanges()

  End Sub

  你可以運行測試一下你建立的這個WebService它將提供兩個方法返回的DataSet是以XML表示的

  業務層的完整代碼如下

  Imports SystemWebServices

  Public Class Service

  Inherits SystemWebServicesWebService

  Web Services Designer Generated Code……

  <WebMethod()> Public Function Get_Dataset() As super_ds

  customer_daFill(Super_dsCustomers)

  order_daFill(Super_dsOrders)

  Return Super_ds

  End Function

  <WebMethod()> Public Sub Update_Dataset()

  Super_dsAcceptChanges()

  End Sub

   WEB SERVICE EXAMPLE

   The HelloWorld() example service returns the string Hello World

   To build uncomment 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

  第二步創建表示層

  具體步驟如下

   新建一個Windows應用程序命名為Windows Form For 表示層

   在窗體上添加一個DataGrid一個ButtonButton的text為Load作用是從業務層讀取數據

   在解決方案窗體中添加Web 引用將我們自己建立的Web Service for 業務層引入到當前項目中

   向Button的Click事件添加如下代碼

  Dim Customer_Ds As New localhostsuper_ds()

  Dim ser As New localhostService()

  Customer_DsMerge(serGet_Dataset)

  DataGridDataSource = Customer_Ds

  這裡我們調用了Web Service的Get_DataSet函數Update_DataSet方法的調用與此完全相同

  表示層的完整代碼如下

  Imports Data_Access_表示層

  Public Class Form

  Inherits SystemWindowsFormsForm

  #Region Windows Form Designer generated code

  Public Sub New()

  MyBaseNew()

  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 component list

  Protected Overloads Overrides Sub Dispose(ByVal disposing As Boolean)

  If disposing Then

  If Not (components Is Nothing) Then

  componentsDispose()

  End If

  End If

  MyBaseDispose(disposing)

  End Sub

  Friend WithEvents Button As SystemWindowsFormsButton

  Friend WithEvents Button As SystemWindowsFormsButton

  Friend WithEvents Button As SystemWindowsFormsButton

  Friend WithEvents Client_DataSet As Data_Access_表示層localhostsuper_ds

  Friend WithEvents DataGrid As SystemWindowsFormsDataGrid

  Required by the Windows Form Designer

  Private components As SystemComponentModelContainer

  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

  <SystemDiagnosticsDebuggerStepThrough()> Private Sub InitializeComponent()

  MeButton = New SystemWindowsFormsButton()

  MeButton = New SystemWindowsFormsButton()

  MeButton = New SystemWindowsFormsButton()

  MeClient_DataSet = New Data_Access_表示層localhostsuper_ds()

  MeDataGrid = New SystemWindowsFormsDataGrid()

  CType(MeClient_DataSet SystemComponentModelISupportInitialize)BeginInit()

  CType(MeDataGrid SystemComponentModelISupportInitialize)BeginInit()

  MeSuspendLayout()

  

  Button

  

  MeButtonLocation = New SystemDrawingPoint(

  MeButtonName = Button

  MeButtonTabIndex =

  MeButtonText = load

  

  Button

  

  MeButtonLocation = New SystemDrawingPoint(

  MeButtonName = Button

  MeButtonTabIndex =

  MeButtonText = update

  

  Button

  

  MeButtonLocation = New SystemDrawingPoint(

  MeButtonName = Button

  MeButtonTabIndex =

  MeButtonText = clear

  

  Client_DataSet

  

  MeClient_DataSetDataSetName = Client_DataSet

  MeClient_DataSetLocale = New SystemGlobalizationCultureInfo(zhCN

  MeClient_DataSetNamespace =

  

  DataGrid

  

  MeDataGridDataMember =

  MeDataGridLocation = New SystemDrawingPoint(

  MeDataGridName = DataGrid

  MeDataGridSize = New SystemDrawingSize(

  MeDataGridTabIndex =

  

  Form

  

  MeAutoScaleBaseSize = New SystemDrawingSize(

  MeClientSize = New SystemDrawingSize(

  MeControlsAddRange(New SystemWindowsFormsControl() {MeDataGrid MeButton MeButton MeButton})

  MeName = Form

  MeText = Form

  CType(MeClient_DataSet SystemComponentModelISupportInitialize)EndInit()

  CType(MeDataGrid SystemComponentModelISupportInitialize)EndInit()

  MeResumeLayout(False)

  End Sub

  #End Region

  Private Sub Button_Click(ByVal sender As SystemObject ByVal e As SystemEventArgs) Handles ButtonClick

  Dim Customer_Ds As New localhostsuper_ds()

  Dim ser As New localhostService()

  Customer_DsMerge(serGet_Dataset)

  DataGridDataSource = Customer_Ds

  End Sub

  End Class

  總結可見表示層窗體上完全沒有數據庫連接控件它與數據庫的連接任務是通過業務層來完成的這樣程序的結構更加清晰當然業務層的實現也可以用其他方法比如寫一個自己的類來完成與數據庫的數據傳輸


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