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Visual Studio 2005 初体验之三：使用DBFactory class连接数据库

        在以前开发的项目中，连接到不同的数据源需要使用不同的代码，VS2005中的DBFactory class则可以完成对不同数据源的连接使用相同的代码。因此，如果在一个项目中需要使用多个数据源（如Access、SQLServer、Foxpro等），那么VS2005为开发者提供了很好的途径。

       

实例：

 

1、新建一个工程，按照图示的要求布置界面。

2、GetData button click事件的代码：

 

2.1、获得使用的数据库名称：

        Dim myName As String = providerComboBox.SelectedItem.ToString()

 

2.2、定义连接数据库对象：

        Dim myConnectionSettings As ConnectionStringSettings = ConfigurationManager.ConnectionStrings(myName)

        Dim myProvider As DbProviderFactory = DbProviderFactories.GetFactory(myConnectionSettings.ProviderName)

        Dim myConnection As DbConnection = myProvider.CreateConnection()

        myConnection.ConnectionString = myConnectionSettings.ConnectionString

 

2.3、打开数据库连接对象：

        myConnection.Open()

 

2.4、为datagrid定义一个数据集：

        Dim myAdapter As DbDataAdapter = myProvider.CreateDataAdapter()
         Dim myCommand As DbCommand = myProvider.CreateCommand()

         Dim myQuery As String = "SELECT * FROM SampleData"
         Dim myDataSet As DataSet = New DataSet()

         myCommand.Connection = myConnection
         myCommand.CommandText = myQuery

         myAdapter.SelectCommand = myCommand

         myAdapter.Fill(myDataSet)

 

2.5、绑定datagrid：

         displayDataGridView.DataSource = myDataSet.Tables(0)

 

3、获得服务器和数据库连接字符串信息：

        providerNameTextLabel.Text = "Provider: " & myConnectionSettings.ProviderName.ToString()
         connectionStringLabel.Text = "ConnectString:" & myConnectionSettings.ConnectionString.ToString()

 

4、完整的代码如下：

Imports System
Imports System.Collections.Generic
Imports System.ComponentModel
Imports System.Data
Imports System.Drawing
Imports System.Text
Imports System.Windows.Forms
Imports System.Data.Common
Imports System.Configuration
Imports System.Diagnostics

 

Public Class factoryClassesForm

    Private Sub getDataButton_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles getDataButton.Click
        Try

            '' Get the name of the database we are going to use
            Dim myName As String = providerComboBox.SelectedItem.ToString()

            '' Get the connection settings from the configuration file based on the name selected
            '' in the ComboBox
            Dim myConnectionSettings As ConnectionStringSettings = ConfigurationManager.ConnectionStrings(myName)

            '' Create an instance of the DbProviderFactory by using the Provider name in the config file
            Dim myProvider As DbProviderFactory = DbProviderFactories.GetFactory(myConnectionSettings.ProviderName)

            '' Create the connection from the DbProvider factory, this code does not need to change for
            '' for different providers
            Dim myConnection As DbConnection = myProvider.CreateConnection()

            '' Get the connection string from the connectionsettings
            '' This gets us the specific provider by which we will connect
            myConnection.ConnectionString = myConnectionSettings.ConnectionString

            '' Open the connection
            myConnection.Open()

            '' now we can create the DataAdapter and then create a command
            Dim myAdapter As DbDataAdapter = myProvider.CreateDataAdapter()
            Dim myCommand As DbCommand = myProvider.CreateCommand()

            '' Create the DataSet so that we can populate the datagrid
            Dim myQuery As String = "SELECT * FROM SampleData"
            Dim myDataSet As DataSet = New DataSet()
            myCommand.Connection = myConnection
            myCommand.CommandText = myQuery
            myAdapter.SelectCommand = myCommand
            myAdapter.Fill(myDataSet)

            displayDataGridView.DataSource = myDataSet.Tables(0)

            '' with other provider and connection string information
            providerNameTextLabel.Text = "Provider: " & myConnectionSettings.ProviderName.ToString()
            connectionStringLabel.Text = "ConnectString:" & myConnectionSettings.ConnectionString.ToString()
        Catch ex As Exception
            MessageBox.Show("There was an error retrieving data.  Please try again.", "Alert")
        End Try
    End Sub

 

    Private Sub factoryClassesForm_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        providerComboBox.SelectedIndex = 0
    End Sub

End Class

 

5、运行后的效果如图：