How To Open ADO Recordsets Asynchronously Using WithEvents

MORE INFORMATION

The following example uses the Pubs database that ships with SQL Server to demonstrate the opening of asynchronous ADO recordsets from within Visual Basic 6.0.

The example repeatedly opens and closes ADO recordsets until the user selects Cancel. The sample assumes that the Pubs sample database is used for this project and that the database contains the Publishers, Titles, and Authors tables.

To create the example, use the following steps:

Step-by-Step Example

1. Create a new Standard.exe Visual Basic 6.0 project.
2. From the Project menu, choose References and add the Microsoft ActiveX Data Objects Library reference to the project.
3. Add two command buttons to Form1, the project's default form.
4. Cut and paste the following code into the project:

      Option Explicit
   
      Dim WithEvents con As ADODB.Connection
      Dim rst As New ADODB.Recordset
      Dim iExecutionCount As Integer
   
      Private Sub Form_Load()
   
         Dim sConnect As String
         Dim sServer As String
         Dim sUID As String
         Dim sPWD As String
   
         On Error GoTo EH
   
         ' Specify connection parameters.
   
         sServer = "<your server name>"
         sUID = "<your SQL Server user ID>"
         sPWD = "<your SQL Server user ID password>"
   
         sConnect = "Driver={SQL Server};Server=" & sServer & _
                 ";Database=Pubs;"
         sConnect = sConnect & "UID=" & sUID & ";"
         sConnect = sConnect & "PWD=" & sPWD & ";DSN='';"
         Set con = New ADODB.Connection
         con.CursorLocation = adUseClient
   
         ' Open the connection.
   
         con.Open sConnect
   
         command1.Caption = "Open Recordsets"
         command2.Caption = "Cancel"
         Exit Sub
   
       EH:
       MsgBox "Could not establish ODBC connection.", vbCritical + vbOKOnly
       Set con = Nothing
       End
   
      End Sub
   
     Private Sub Form_QueryUnload(Cancel As Integer, UnloadMode As Integer)
   
      On Error Resume Next
      rst.Close
      Set rst = Nothing
      Set con = Nothing
   
      End Sub
   
      Private Sub Command1_Click()
   
      ' This code begins the process of repeatedly opening ADO recordsets.
   
      command1.Enabled = False
      command2.Enabled = True
      GetRecordsetData
   
      End Sub
   
      Private Sub Command2_Click()
   
      ' This code ends the process of repeatedly opening ADO recordsets.
   
      On Error Resume Next
      rst.Close
      MsgBox "The recordset was opened " & iExecutionCount & " time(s)."
      iExecutionCount = 0
      command1.Enabled = True
      command2.Enabled = False
   
      End Sub
   
      Private Sub GetRecordsetData()
   
      iExecutionCount = iExecutionCount + 1
      If rst.State <> adStateClosed Then
         rst.Close
      End If
      rst.Open _
         "Select * From Pubs..Publishers, Pubs..Titles, Pubs..Authors", _
         con, adOpenKeyset, adLockOptimistic, adAsyncExecute
   
      End Sub
   
       Private Sub con_ExecuteComplete(ByVal RecordsAffected As Long, _
       ByVal pError As ADODB.Error, adStatus As ADODB.EventStatusEnum, _
       ByVal pCommand As ADODB.Command, _
       ByVal pRecordset As ADODB.Recordset, _
       ByVal pConnection As ADODB.Connection)
   
      ' When the ADO recordset has been populated with data, begin opening
      ' the next ADO recordset.
      GetRecordsetData
   
      End Sub
   					

5. Change the values of sServer, sUID, and sPWD in the Form_Load event of Form1 to valid values for your SQL Server environment.
6. Run the project. Click Open Recordsets to begin the asynchronous opening and closing of the ADO resultsets.
7. Select Cancel to stop opening the ADO recordsets. A message box displays telling you how many ADO recordsets were opened.