How To Open ADO Recordsets Asynchronously Using WithEvents

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Article ID: 190988 - View products that this article applies to.
This article was previously published under Q190988
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SUMMARY

This article describes how to take advantage of asynchronous ActiveX Data Objects (ADO) functionality in Visual Basic 6.0. ADO gives developers the ability to declare ADO object variables with the WithEvents keyword, which provides enhanced control over asynchronous operations.

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.

Properties

Article ID: 190988 - Last Review: March 2, 2005 - Revision: 1.3
APPLIES TO
  • Microsoft ActiveX Data Objects 2.0
  • Microsoft ActiveX Data Objects 2.1 Service Pack 2
  • Microsoft ActiveX Data Objects 2.5
  • Microsoft ActiveX Data Objects 2.6
  • Microsoft ActiveX Data Objects 2.7
  • Microsoft Visual Basic Enterprise Edition for Windows 6.0
Keywords: 
kbdatabase kbhowto KB190988

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