Excel VBA QueryTable callback function after table refresh [duplicate] - multithreading

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Excel VBA - QueryTable AfterRefresh function not being called after Refresh completes
(2 answers)
Closed 5 years ago.
I am writing/maintaining an Excel VBA application where there are multiple QueryTables linked to MS sql server databases. Users of the application can alter the SQL query to each table by manipulating various UI controls on the Excel document.
One of the issues I have come across with QueryTables is there use of multi threading. Each QueryTable on the document has an original state that must be restored after a query is ran. For instance, if QueryTable1 had a base query of
Select * from example_table
and the user selected certain inputs on the controls to create
Select * from example_table Where object_oid = '10'
I would need the original state to be restored. The code below is a snapshot of how I am currently accomplishing this
Sub RefreshDataQuery()
'Dependencies: Microsoft Scripting Runtime (Tools->References) for Dictionary (HashTable) object
Dim querySheet As Worksheet
Dim interface As Worksheet
Set querySheet = Worksheets("QTable")
Set interface = Worksheets("Interface")
Dim sh As Worksheet
Dim qt As QueryTable
Dim qtDict As New Scripting.Dictionary
Set qtDict = UtilFunctions.CollectAllQueryTablesToDict
Set qt = qtDict.Item("Query from fred2")
''' Building SQL Query String '''
Dim sqlQueryString As String
Dim originalQueryCache As String
originalQueryCache = qt.CommandText
sqlQueryString = qt.CommandText
QueryBuilder.BuildSQLQueryStringFromInterface interface, sqlQueryString
MsgBox sqlQueryString
qt.CommandText = sqlQueryString
If Not qt Is Nothing Then
qt.Refresh
Else
'Error Messages and handling here
' Cut out to keep code short
End If
''' CLEAN UP '''
'Restore the original base SQL query
' Problem is here
' This, or any other altering statement, will error out if the query is still refreshing
qt.CommandText = originalQueryCache
' Other original state restoring code below...
' Free the dictionary
Set qtDict = Nothing
End Sub
Ideally, if I was writing this in another modern language, I would create a callback function or run the refresh in my own thread with a completion notifier. I spent a good chunk of time researching how to get a callback function for the qt.Refresh call, but am having no luck. I realize I could 'hack' around this a bit but I would prefer to not engage in bad practices as many people will have to maintain this in the future.
This application must support Excel 2010 versions and upward
So how can I create a callback function for VBA functions that are run in separate threads? Or, should I be looking at another approach?

Answer 1

The QueryTables events aren't exposed except through a custom class module and the WithEvents keyword. First, create a custom class module named CQtEvents and put this in it:
Private WithEvents mQryTble As QueryTable
Private msOldSql As String
Public Property Set QryTble(ByVal QryTble As QueryTable): Set mQryTble = QryTble: End Property
Public Property Get QryTble() As QueryTable: Set QryTble = mQryTble: End Property
Public Property Let OldSql(ByVal sOldSql As String): msOldSql = sOldSql: End Property
Public Property Get OldSql() As String: OldSql = msOldSql: End Property
Private Sub mQryTble_AfterRefresh(ByVal Success As Boolean)
Me.QryTble.CommandText = Me.OldSql
End Sub
That's two properties: one to hold the QueryTable and one to store the old sql. Then your procedure would look something like
Sub RefreshDataQuery()
Dim interface As Worksheet
Dim qt As QueryTable
Dim qtDict As New Scripting.Dictionary
Dim clsQtEvents As CQtEvents
Dim sqlQueryString As String
Set qtDict = UtilFunctions.CollectAllQueryTablesToDict
Set qt = qtDict.Item("Query from fred2")
sqlQueryString = qt.CommandText
QueryBuilder.BuildSQLQueryStringFromInterface interface, sqlQueryString
'Create class for events and store old sql
Set clsQtEvents = New CQtEvents
Set clsQtEvents.QryTble = qt
clsQtEvents.OldSql = qt.CommandText
qt.CommandText = sqlQueryString
If Not qt Is Nothing Then
qt.Refresh 'after this is done, the event in the class will fire
Else
'Error Messages and handling here
End If
End Sub
Because you define mQryTble with WithEvents, its two events (BeforeRefresh and AfterRefresh) are exposed in the class. By setting CQtEvents.QryTble to your QueryTable, the class then listens for events on that QueryTable. The CommandText is stored in OldSql before it's changed. Then when the Refresh is done, the event fires and the CommandText is restored. Of course not Refresh is done in the event, but I assume you want the old sql statement in there if it's refreshed or reprocessed.
Next, you should consider making a collection class to hold a bunch of QtEvents instances. I presume your code processes one as an example, but you're really doing more. Then you can move your CollectAllQueryTables inside that collection class and move the BuildSQL part inside the CQtEvents class.