Cancel-Methode – Beispiel (VB)
In diesem Beispiel wird die Cancel-Methode verwendet, um einen Befehl abzubrechen, der auf einem Connection-Objekt ausgeführt wird, wenn die Verbindung stark ausgelastet ist.
'BeginCancelVB
'To integrate this code
'replace the data source and initial catalog values
'in the connection string
Public Sub Main()
On Error GoTo ErrorHandler
'recordset and connection variables
Dim Cnxn As ADODB.Connection
Dim strCnxn As String
Dim strCmdChange As String
Dim strCmdRestore As String
'record variables
Dim blnChanged As Boolean
' Open a connection
Set Cnxn = New ADODB.Connection
strCnxn = "Provider='sqloledb';Data Source='MySqlServer';" & _
"Initial Catalog='Pubs';Integrated Security='SSPI';"
Cnxn.Open strCnxn
' Define command strings
strCmdChange = "UPDATE titles SET type = 'self_help' WHERE type = 'psychology'"
strCmdRestore = "UPDATE titles SET type = 'psychology' " & _
"WHERE type = 'self_help'"
' Begin a transaction, then execute a command asynchronously
Cnxn.BeginTrans
Cnxn.Execute strCmdChange, , adAsyncExecute
' do something else for a little while -
' use i = 1 to 32000 to allow completion
Dim i As Integer
For i = 1 To 1000
i = i + i
Debug.Print i
Next i
' If the command has NOT completed, cancel the execute and
' roll back the transaction; otherwise, commit the transaction
If CBool(Cnxn.State And adStateExecuting) Then
Cnxn.Cancel
Cnxn.RollbackTrans
blnChanged = False
MsgBox "Update canceled."
Else
Cnxn.CommitTrans
blnChanged = True
MsgBox "Update complete."
End If
' If the change was made, restore the data
' because this is only a demo
If blnChanged Then
Cnxn.Execute strCmdRestore
MsgBox "Data restored."
End If
' clean up
Cnxn.Close
Set Cnxn = Nothing
Exit Sub
ErrorHandler:
If Not Cnxn Is Nothing Then
If Cnxn.State = adStateOpen Then Cnxn.Close
End If
Set Cnxn = Nothing
If Err <> 0 Then
MsgBox Err.Source & "-->" & Err.Description, , "Error"
End If
End Sub
'EndCancelVB