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Tip of the Day
Language: Visual Basic
Expertise: Advanced
Jun 29, 2000

Use Asynchronicity for Speed

If you need to run a complicated query that returns a large recordset, ADO 2.1 gives you the best of both worlds. Sometimes you just need to put a recordset into an AddItem type grid, or prepare it for a report. So, if you need to process the recordset as soon as the first record is fetched, you should start processing in the Execute_Complete event of the connection object. If you can also use a disconnected recordset, you can set the ActiveCon-nection property equal to nothing. This code might be the fastest way to process a large recordset with ADO:
 
Private WithEvents m_adoConEvent As ADODB.Connection
' the RS that enables the event Fetch_Complete 
' to be fired off Attribute 
Private WithEvents m_adoRstEvent As ADODB.Recordset 
Private Sub GetRecordSet()
	Dim sSQL As String 
	'A large or complicated SQL statemtent
	sSQL = "select a large complicate query"
	Set m_adoConEvent = New ADODB.Connection
	Set m_adoRstEvent = New ADODB.Recordset 
	m_adoConEvent.Open "Connection String"
	m_adoRstEvent.CursorLocation = adUseClient
	Me.Caption = "Started" 
	'Do something to tell the user where the process is 
	'at. Have the command execute and fetch at the same 
	'time without interrupting workflow.
	m_adoRstEvent.Open sSQL, m_adoConEvent, _
		adOpenStatc, adLockReadOnly, adCmdText _
		Or adAsyncFetch Or adAsyncExecute 
End Sub
Private Sub m_adoConEvent_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)
	Do Until pRecordset.EOF
		'start processing the recordset
	Loop
End Sub
Private Sub m_adoRstEvent_FetchComplete(ByVal pError _
	As ADODB.Error, adStatus As ADODB.EventStatusEnum, _
	ByVal pRecordset As ADODB.Recordset)
	Set pRecordset.ActiveConnection = Nothing 
	'this will speed processing time
End Sub
Private Sub m_adoRstEvent_FetchProgress(ByVal Progress _
	As Long, ByVal MaxProgress As Long, _
	adStatus As ADODB.EventStatusEnum, ByVal _
	pRecordset As ADODB.Recordset)
	'let the user know work is happening
End Sub
By using both adAsyncFetch and adAsyncExecute, you can start processing even while you're returning data.
Darren McBratney
 
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