Tài liệu Using the Connection Object pptx

Using the Connection Object As with ADO.NET, you will be using the Connection object to set up a connection to the database of your choice.. As you get started looking at the different e

Using the Connection Object

As with ADO.NET, you will be using the Connection object to set up a connection to the database of your choice

As you get started looking at the different examples, take a look at the main form that will be used to launch each of them, shown in Figure A.3

Figure A.3 This form, called frmMain, is the Main form that is used for the

examples in this Appendix

The button that is used for this example is called btnOpenConn, and the following is the code used for the Click event, shown here in Listing A.1

Listing A.1 frmMain.vb: Code for Calling the Routine to Open and Display the ADO Connection

Private Sub btnOpenConn_Click(ByVal sender As System.Object, _

ByVal e As System.EventArgs) Handles btnOpenConn.Click

OpenAndDisplayADOConnection(Me.txtCurrentResults)

End Sub

Each of the buttons calls examples, passing the text box called txtCurrentResults This text box is located at the bottom of the form For clarity, the examples have been grouped

in modules by section In this case, the first example routine, called

OpenAndDisplayADOConnection, can be found in basConnectionExamples.vb The code for this routine is shown in Listing A.2

Listing A.2 basConnectionExamples.vb: Code for Opening and Displaying the ADO Connection

Sub OpenAndDisplayADOConnection(ByVal txtResults As TextBox)

Dim cnnNet As New ADODB.Connection()

Dim strConnect As String = _

"Provider=SQLOLEDB.1;Integrated Security=SSPI;" &

"Persist Security Info=False;Initial Catalog=Northwind;Data Source=(local)" cnnNet.Open(strConnect)

txtResults.Text = "New connection string : " & _

vbCrLf & vbCrLf & cnnNet.ConnectionString

cnnNet.Close()

End Sub

As you can see from this example, using the ADO Connection object is virtually the same

as ADO.NET You can see this example being executed in Figure A.4

Figure A.4 The text displayed here is the connection string that was set

Listing A.3 provides two other examples of using the connection object, also found in basConnectionExamples.vb The first is code to open a connection to a Jet database by using a workgroup file, username, and password The second is to open a Jet version of the Northwind database

Listing A.3 basConnectionExamples.vb: Two Examples of Opening Jet Databases

Sub DisplayProviderAndSecuredAccessDB(ByVal txtResults As TextBox)

Dim cnnNet As New ADODB.Connection()

cnnNet.Provider = "Microsoft.Jet.OLEDB.4.0"

cnnNet.Properties("Jet OLEDB:System database").Value = _

"c:\Books\VBNETHowTo\Examples\AppA\MySystem.mdw"

cnnNet.Open("Data

Source=c:\Books\VBNETHowTo\Examples\AppA\MyMDB.mdb;" &

"User Id=Admin;Password=MyPW")

txtResults.Text = cnnNet.ConnectionString

End Sub

Sub OpenNorthwindADOConnection(ByRef cnnCurr As ADODB.Connection)

Dim strConnect As String = "Provider=SQLOLEDB.1;Integrated Security=SSPI;" & "Persist Security Info=False;Initial Catalog=Northwind;Data

Source=(local)"

Try

cnnCurr.Open(strConnect)

Catch expADO As Exception

MessageBox.Show("The following error occurred: " & expADO.Message)

End Try

End Sub

In the last routine, you can also see how to use the Try…Catch…End Try block to trap any exceptions that might occur Next you will see how to use the Connection object with the Recordset object in VB NET