Q170536: HOWTO: Use API to Customize DAO Registry to Close ODBC Connectn
Article: Q170536
Product(s): Microsoft Visual Basic for Windows
Version(s): 5.0,6.0
Operating System(s):
Keyword(s): kbVBp kbVBp500 kbVBp600 kbOSWin98 kbGrpDSVBDB kbDSupport kbMDACNoSweep kbATM
Last Modified: 23-AUG-2001
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The information in this article applies to:
- Microsoft Visual Basic Professional Edition for Windows, versions 5.0, 6.0
- Microsoft Visual Basic Enterprise Edition for Windows, versions 5.0, 6.0
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SUMMARY
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In DAO, using the Close method on a database opened with ODBC drivers does not
close the database; a cached connection remains idle before timing out. The
default duration of this timeout is 600 seconds (10 minutes). If your
application cannot accept the default behavior, you could control this time-out
period by customizing the ConnectionTimeout value in Windows registry setting.
MORE INFORMATION
================
You can control the duration of ConnectionTimeout by creating a
ConnectionTimeout registry entry for Jet. In Windows NT 3.51, the type is called
"REG_DWORD"; in Windows 95, Windows 98, Windows Me (with DAO JET 3.6), Windows
2000, and Windows NT 4.0, the type is called "DWORD." "REG_DWORD" and "DWORD"
are different terms referring to the same thing, a 32-bit number.
Although Visual Basic includes the SaveSetting and GetSetting functions to save
and retrieve information from the registry, entries of types other than "REG_SZ"
("String" for Windows 95, Windows 98, Windows 2000, and Windows NT4.0) are not
recognized. This article demonstrates how to use the registry API to set the DAO
ConnectionTimeout setting to 1, which closes the connection after the Close
method with only a one-second delay.
Sample Program
--------------
The following example has three CommandButton controls:
- Command1 creates a testing Registry entry
"Software\MyApp\Jet\3.5\Engines\ODBC" under HKEY_LOCAL_MACHINE root key, and
sets the ConnectionTimeOut value to 1.
- Command2 establishes the connection by opening the Pubs database.
- Command3 closes the database.
You can check the detailed connection information by executing SP_WHO stored
procedure on the SQL Server, then open/close database with/without the registry
entry created.
1. Start a new project in Visual Basic and choose "Standard EXE." Form1 is
created by default.
2. Reference the Microsoft DAO 3.5 Object Library under Project, References menu
items.
3. Add three CommandButtons, Command1, Command2, and Command3 to Form1.
4. Paste the following code into the General Declarations section of Form1:
Option Explicit
Dim ws As Workspace
Dim db As Database
Dim TimeOutValue As Integer
Private Sub CreateNewKey(sNewKeyName As String, lPredefinedKey As Long)
Dim hNewKey As Long 'handle to the new key
Dim lRetVal As Long 'result of the RegCreateKeyEx function
lRetVal = RegCreateKeyEx(lPredefinedKey, sNewKeyName, 0&, _
vbNullString, REG_OPTION_NON_VOLATILE, KEY_ALL_ACCESS, _
0&, hNewKey, lRetVal)
RegCloseKey (hNewKey)
End Sub
Private Sub SetKeyValue(sKeyName As String, sValueName As String, _
vValueSetting As Variant)
Dim lRetVal As Long 'result of the SetValueExLong function
Dim hKey As Long 'handle of open key
lRetVal = RegOpenKeyEx(HKEY_LOCAL_MACHINE, sKeyName, 0, _
KEY_ALL_ACCESS, hKey)
lRetVal = RegSetValueExLong(hKey, sValueName, 0&, _
REG_DWORD, vValueSetting, 4)
RegCloseKey (hKey)
End Sub
Private Function QueryValue(sKeyName As String, sValueName As String) _
As Integer
Dim lRetVal As Long 'result of the API functions
Dim hKey As Long 'handle of opened key
Dim vValue As Variant 'setting of queried value
lRetVal = RegOpenKeyEx(HKEY_LOCAL_MACHINE, sKeyName, 0, _
KEY_ALL_ACCESS, hKey)
lRetVal = QueryValueEx(hKey, sValueName, vValue)
If lRetVal = ERROR_NONE Then
QueryValue = True
TimeOutValue = vValue
Else
QueryValue = False
End If
RegCloseKey (hKey)
End Function
Private Sub Command1_Click()
If QueryValue("Software\MyApp\Jet\3.5\Engines\ODBC", _
"ConnectionTimeout") Then
If TimeOutValue <> 1 Then
SetKeyValue "Software\MyApp\Jet\3.5\Engines\ODBC", _
"ConnectionTimeout", 1
End If
MsgBox "Test registry key already set"
Else
CreateNewKey "Software\MyApp\Jet\3.5\Engines\ODBC", _
HKEY_LOCAL_MACHINE
SetKeyValue "Software\MyApp\Jet\3.5\Engines\ODBC", _
"ConnectionTimeout", 1
MsgBox "Test registry key created successfully"
End If
End Sub
Private Sub Command2_Click()
Dim strConnect As String
DBEngine.IniPath = "HKEY_LOCAL_MACHINE\Software\MyApp\Jet\3.5"
Set ws = DBEngine.Workspaces(0)
strConnect = "ODBC;SERVER=MyServer;" & _
"DRIVER={SQL SERVER};DATABASE=pubs;UID=sa;PWD=;"
Set db = ws.OpenDatabase("", False, False, strConnect)
MsgBox "Connection established"
End Sub
Private Sub Command3_Click()
If db Is Nothing Then
MsgBox "Already Disconnected"
Exit Sub
End If
db.Close
ws.Close
Dim Start As Long
Start = Timer
Do
DBEngine.Idle dbFreeLocks
DoEvents
Loop While Timer <= Start + 1
MsgBox "Disconnected"
End Sub
Private Sub Form_Load()
Command1.Caption = "Create/Set test registry entry"
Command2.Caption = "Open database"
Command3.Caption = "Close database"
End Sub
5. From the Project menu, select Add Module, then click Module. Copy and paste
the following code into the General Declarations section of Module1:
Option Explicit
Global Const REG_DWORD As Long = 4
Global Const HKEY_LOCAL_MACHINE = &H80000002
Global Const ERROR_NONE = 0
Global Const KEY_ALL_ACCESS = &H3F
Global Const REG_OPTION_NON_VOLATILE = 0
Global TimeOut As Integer
Declare Function RegCloseKey Lib "advapi32.dll" _
(ByVal hKey As Long) As Long
Declare Function RegCreateKeyEx Lib "advapi32.dll" Alias _
"RegCreateKeyExA" (ByVal hKey As Long, ByVal lpSubKey As String, _
ByVal Reserved As Long, ByVal lpClass As String, ByVal dwOptions _
As Long, ByVal samDesired As Long, ByVal lpSecurityAttributes _
As Long, phkResult As Long, lpdwDisposition As Long) As Long
Declare Function RegOpenKeyEx Lib "advapi32.dll" Alias _
"RegOpenKeyExA" (ByVal hKey As Long, ByVal lpSubKey As String, _
ByVal ulOptions As Long, ByVal samDesired As Long, phkResult As _
Long) As Long
Declare Function RegQueryValueExLong Lib "advapi32.dll" Alias _
"RegQueryValueExA" (ByVal hKey As Long, ByVal lpValueName As _
String, ByVal lpReserved As Long, lpType As Long, lpData As _
Long, lpcbData As Long) As Long
Declare Function RegQueryValueExNULL Lib "advapi32.dll" Alias _
"RegQueryValueExA" (ByVal hKey As Long, ByVal lpValueName As _
String, ByVal lpReserved As Long, lpType As Long, ByVal lpData _
As Long, lpcbData As Long) As Long
Declare Function RegSetValueExLong Lib "advapi32.dll" Alias _
"RegSetValueExA" (ByVal hKey As Long, ByVal lpValueName As String, _
ByVal Reserved As Long, ByVal dwType As Long, lpValue As Long, _
ByVal cbData As Long) As Long
Function QueryValueEx(ByVal lhKey As Long, ByVal szValueName As _
String, vValue As Variant) As Long
Dim cch As Long
Dim lrc As Long
Dim lType As Long
Dim lValue As Long
Dim sValue As String
On Error GoTo QueryValueExError
lrc = RegQueryValueExNULL(lhKey, szValueName, 0&, lType, 0&, cch)
If lrc <> ERROR_NONE Then Error 5
lrc = RegQueryValueExLong(lhKey, szValueName, 0&, lType, _
lValue, cch)
If lrc = ERROR_NONE Then vValue = lValue
QueryValueExExit:
QueryValueEx = lrc
Exit Function
QueryValueExError:
Resume QueryValueExExit
End Function
6. Make sure to change your SERVER, UID, and PWD parameters in the connection
string under Command2_Click.
7. Start the program or press the F5 key.
8. You can observe the connection information by executing the SP_WHO stored
procedure at SQL Server. Compare the result before and after opening a
database and before and after closing the database.
NOTE: Modify the Jet Engine version in the code, from 3.5 to a higher number, in
order to work with the required version of the Jet Engine.
Starting with Microsoft Data Access Components (MDAC) version 2.6, MDAC no longer
contains the following Jet components:
- Microsoft Jet
- Microsoft Jet OLE DB Provider
- ODBC Desktop Database Drivers
For additional information, click the article number below to view the article in
the Microsoft Knowledge Base:
Q239114 ACC2000: Updated Version of Microsoft Jet 4.0 Available in Download
Center
The "MDAC 2.5 Stack and Windows File Protection" white paper contains a full list
of the components that are shipped with MDAC 2.5, along with a discussion of
Windows File Protection. Refer to this white paper for more information about
the Jet dynamic-link libraries (DLLs) that are included in MDAC 2.5, which are
no longer a part of MDAC 2.6.
For more information about MDAC 2.5 and Windows File Protection, see the
following Microsoft Web site:
http://www.microsoft.com/data/mdacwfp.htm
REFERENCES
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For additional information, please see the following articles in the Microsoft
Knowledge Base:
Q145679 HOWTO: Use the Registry API to Save and Retrieve Setting
Q110227 PRB: ODBC Database Remains Open After a Close Method Used
Additional query words:
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Keywords : kbVBp kbVBp500 kbVBp600 kbOSWin98 kbGrpDSVBDB kbDSupport kbMDACNoSweep kbATM
Technology : kbVBSearch kbAudDeveloper kbZNotKeyword6 kbZNotKeyword2 kbVB500Search kbVB600Search kbVB500 kbVB600
Version : :5.0,6.0
Issue type : kbhowto
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