ACC: How to Relink Back-End Tables with Common Dialog Control
ID: Q181076
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The information in this article applies to:
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Microsoft Access versions 7.0, 97
SUMMARY
Advanced: Requires expert coding, interoperability, and multiuser skills.
This article shows you how to use the Common Dialog control to refresh
linked tables in your database. The Common Dialog control is available with
the Microsoft Office 97 Developer Edition Tools or the Microsoft Access Developer's Toolkit version 7.0. The tables being linked may reside in one or many back-end databases.
For an example of a different method to relink tables that uses Windows
application programming interface (API) functions, refer to the Developer
Solutions sample application (Solutions.mdb) included with Microsoft Access
7.0 and 97. Open the Solutions.mdb database, select "Use multiple
databases" in the "Select a Category of Examples" box, and then "Link
tables at startup" in the Select An Example box.
This article assumes that you are familiar with Visual Basic for
Applications and with creating Microsoft Access applications using the
programming tools provided with Microsoft Access. For more information
about Visual Basic for Applications, please refer to your version of the
"Building Applications with Microsoft Access" manual.
MORE INFORMATION
An application that uses split database design has its tables in one
database in a shared network location (the back-end database), and all its
queries, forms, reports, macros, and modules in another database on each
client computer (the front-end database). The front-end database links all
of its tables to the back-end database. If the back-end database is moved,
errors occur in your application. You can build functionality into your
application to detect that the back-end database file is missing from its
expected location, and then prompt the user for the new location.
The following example demonstrates a method for relinking table data in
your application. This method creates a form that a user can open to relink
the back-end tables, and optionally uses a form to automatically verify the
back-end link behind the scenes.
This article assumes that you have the Microsoft Common Dialog control,
which is available with the Microsoft Office 97 Developer Edition Tools and
the Microsoft Access Developer's Toolkit version 7.0. If you do not have
this control, skip the Browse() function in the example.
NOTE: If you use the Common Dialog control and you plan to distribute your
database application, you must include the Common Dialog Control file,
Comdlg32.ocx, and its supporting DLLs with your setup files. For more
information about which supporting files to include with ActiveX controls
in Microsoft Office 97 Developer Edition Tools applications, search the
Help Index for "ActiveX controls, files required for." For more information
about which supporting files to include with OLE Custom Controls in
Microsoft Access Developer's Toolkit version 7.0 applications, click the
Help button on the "Add the files that you want your custom Setup program
to copy" screen of the Setup Wizard.
Method to Relink Back-End Database Tables
- Create a new blank database called FrontEnd.mdb.
- On the File menu, point to Get External Data, and then click Link
Tables. Create a link to each of the tables in the sample database
Northwind.mdb.
- Create the following new form not based on any table or query in
Design view:
Form: frmNewDataFile
--------------------------
Text box:
Name: txtFileName
Width: 3"
Common Dialog control:
Name: xDialog
Command button:
Name: cmdBrowse
Caption: Browse...
OnClick: =Browse()
Command button:
Name: cmdLinkNew
Caption: Refresh Links
OnClick: =Processtables()
Command button:
Name: cmdCancel
Caption: Cancel
Cancel: Yes
- On the View menu, click Code.
- Type or paste the following procedure:
Private Sub cmdCancel_Click()
On Error GoTo Err_cmdCancel_Click
MsgBox "Link to new back-end cancelled", vbExclamation, _
"Cancel Refresh Link" ' Give a warning of cancellation.
DoCmd.Close acForm, Me.Name ' Close the form.
Exit_cmdCancel_Click:
Exit Sub
Err_cmdCancel_Click:
MsgBox Err.Description
Resume Exit_cmdCancel_Click
End Sub
- On the Debug menu, click "Compile and Save All Modules" (or in
Microsoft Access 7.0, on the Run menu click "Compile All Modules";
then on the File menu, click "Save All Modules").
- Save the frmNewDataFile form and close it.
- In the Database Window, click the Modules tab,
- Create a new module and type or paste the following code:
Option Compare Database
Dim UnProcessed As New Collection
Option Explicit
Public Function Browse()
' Prompts user for back-end database file name.
On Error GoTo Err_Browse
Dim strFilename As String
Dim oDialog As Object
Set oDialog = [Forms]![frmNewDatafile]!xDialog.Object
With oDialog ' Ask for new file location.
.DialogTitle = "Please Select New Data File"
.Filter = "Access Database(*.mdb;*.mda;*.mde;*.mdw)|" & _
"*.mdb; *.mda; *.mde; *.mdw|All(*.*)|*.*"
.FilterIndex = 1
.ShowOpen
' If user responded, put selection into text box on form.
If Len(.FileName) > 0 Then _
[Forms]![frmNewDatafile]![txtFileName] = .FileName
End With
Exit_Browse:
Exit Function
Err_Browse:
MsgBox Err.Description
Resume Exit_Browse
End Function
Public Sub AppendTables()
Dim db As Database, x As Variant
' Add all linked table names into the Unprocessed Collection.
Set db = CurrentDb
ClearAll
For Each x In db.TableDefs
If Len(x.Connect) > 1 Then
UnProcessed.Add Item:=x.Name, key:=x.Name
End If
Next
End Sub
Public Function ProcessTables()
Dim strTest As String
On Error GoTo Err_BeginLink
' Call procedure to add all linked tables into a collection.
AppendTables
' Test for existence of file name\directory selected in
' Common Dialog Control.
strTest = Dir([Forms]![frmNewDatafile]![txtFileName])
On Error GoTo Err_BeginLink
If Len(strTest) = 0 Then ' File not found.
MsgBox "File not found. Please try again.", vbExclamation, _
"Link to new data file"
Exit Function
End If
' Begin relinking tables.
Relinktables (strTest)
' Check to see if all tables have been relinked.
CheckifComplete
DoCmd.Echo True, "Done"
If UnProcessed.Count < 1 Then
MsgBox "Linking to new back-end data file was successful."
Else
MsgBox "Not All back-end tables were successfully relinked"
End If
DoCmd.Close acForm, [Forms]![frmNewDatafile].Name
Exit_BeginLink:
DoCmd.Echo True
Exit Function
Err_BeginLink:
Debug.Print Err.Number
If Err.Number = 457 Then
ClearAll
Resume Next
End If
MsgBox Err.Description
Resume Exit_BeginLink
End Function
Public Sub ClearAll()
Dim x
' Clear any and all names from the Unprocessed Collection.
For Each x In UnProcessed
UnProcessed.Remove (x)
Next
End Sub
Public Function Relinktables(strFilename As String)
Dim dbbackend As Database, dblocal As Database, ws As Workspace, _
x, y
Dim tdlocal As TableDef
On Error GoTo Err_Relink
Set dbbackend = DBEngine(0).OpenDatabase(strFilename)
Set dblocal = CurrentDb
' If the local linked table name is found in the back-end database
' we're looking at, Recreate & Refresh its connect string, and
' then remove its name from the Unprocessed collection.
For Each x In UnProcessed
If Len(dblocal.TableDefs(x).Connect) > 0 Then
For Each y In dbbackend.TableDefs
If y.Name = x Then
Set tdlocal = dblocal.TableDefs(x)
tdlocal.Connect = ";DATABASE=" & _
Trim([Forms]![frmNewDatafile]![txtFileName])
tdlocal.RefreshLink
UnProcessed.Remove (x)
End If
Next
End If
Next
Exit_Relink:
Exit Function
Err_Relink:
MsgBox Err.Description
Resume Exit_Relink
End Function
Public Sub CheckifComplete()
Dim strTest As String, y As String, notfound As String, x
On Error GoTo Err_BeginLink
' If there are any names left in the unprocessed collection,
' then continue.
If UnProcessed.Count > 0 Then
For Each x In UnProcessed
notfound = notfound & x & Chr(13)
Next
' List the tables that have not yet been relinked.
y = MsgBox("The following tables were not found in " & _
Chr(13) & Chr(13) & [Forms]![frmNewDatafile]!txtFileName _
& ":" & Chr(13) & Chr(13) & notfound & Chr(13) & _
"Select another database that contains the additional tables?", _
vbQuestion + vbYesNo, "Tables not found")
If y = vbNo Then
Exit Sub
End If
' Bring the Common Dialog Control back up.
Browse
strTest = Dir([Forms]![frmNewDatafile]![txtFileName])
If Len(strTest) = 0 Then ' File not found.
MsgBox "File not found. Please try again.", vbExclamation, _
"Link to new data file"
Exit Sub
End If
Debug.Print "Break"
Relinktables (strTest)
Else
Exit Sub
End If
CheckifComplete
Exit_BeginLink:
DoCmd.Echo True ' Just in case of error jump.
DoCmd.Hourglass False
Exit Sub
Err_BeginLink:
Debug.Print Err.Number
If Err.Number = 457 Then
ClearAll
Resume Next
End If
MsgBox Err.Description
Resume Exit_BeginLink
End Sub
- On the Debug menu, click "Compile and Save All Modules" (in Microsoft
Access 7.0, on the Run menu click "Compile All Modules"; then on the
File menu, click "Save All Modules").
- Save the module as RelinkCode and close it.
- Move the Northwind.mdb sample database to another folder on your hard
drive, so the linked tables in FrontEnd.mdb will need to be refreshed.
- Open the frmNewDataFile form, and click the Browse button.
- In the "Please Select New Data File" dialog box, locate Northwind.mdb
in its new folder, and then click Open. Note that the path and file
name of the database appears in the text box on your form.
- Click the Refresh Links button on the form. Note that you receive the
following message when the procedure is done:
Linking to new back-end data file was successful.
Creating a Startup Form to Check Linked Tables
If you want to verify the linked tables automatically each time that you
open the FrontEnd.mdb database, you can follow these steps to create a
hidden form for that purpose:
- Create a new form not based on any table or query in Design view.
- On the View menu, click Code.
- Type the following procedure to execute when the form opens:
Private Sub Form_Open(Cancel As Integer)
' Tests a linked table for valid back-end.
On Error GoTo Err_Form_Open
Dim strTest As String, db As Database
Dim td As TableDef
Set db = CurrentDb
For Each td In db.TableDefs
If Len(td.Connect) > 0 Then ' Is a linked table.
On Error Resume Next ' Turn off error trap.
strTest = Dir(Mid(td.Connect, 11)) ' Check file name.
On Error GoTo err_Form_Open ' Turn on error trap.
If Len(strTest) = 0 Then ' No matching file.
If MsgBox("Couldn't find the back-end file " & _
Mid(td.Connect, 11) & ". Please choose new data _
file.", _
vbExclamation + vbOKCancel + vbDefaultButton1, _
"Can't find backend data file.") = vbOK Then
DoCmd.OpenForm "frmNewDataFile" ' Open prompt form.
Else
MsgBox "The linked tables can't find their source. " & _
"Please log onto network and restart the application."
End If
End If
End If
Next ' Loop to next tabledef.
DoCmd.Close acForm, Me.Name
Exit_Form_Open:
Exit Sub
Err_Form_Open:
MsgBox "Oops! " & Error.Description
Resume Exit_Form_Open
End Sub
- On the Debug menu, click "Compile and Save All Modules" (or in
Microsoft Access 7.0, on the Run menu click "Compile All Modules"; then
on the File menu, click "Save All Modules").
- Save the form as frmCheckLink, and then close it.
- Set frmCheckLink as your Startup form by clicking Startup on the Tools
menu. In the Startup dialog box, select frmCheckLink in the Display
Form box, and then click OK.
- Make frmCheckLink a hidden form by using the right mouse button
(right-click) to click frmCheckLink in the Database window, and then
click Properties on the shortcut menu that appears. Click the Hidden
check box in the frmCheckLink Properties dialog box, and then click OK.
- Move the Northwind.mdb sample database to another folder on your hard
drive, so the linked tables in FrontEnd.mdb will need to be refreshed.
- Close and then reopen FrontEnd.mdb. Note that you receive the following message:
Couldn't find the back-end file <Database Name>. Please choose new
data file.
If you click OK, the frmNewDataFile form opens for you to select a new
back-end database, and then refreshes your table links. If you click
Cancel, you receive this message:
The linked tables can't find their source. Please log onto network
and restart the application.
REFERENCES
For information about customizing the example for refreshing linked tables
in the Developer Solutions sample application (Solution.mdb), please see
the following article in the Microsoft Knowledge Base:
Q154397
ADT/ODE How to Modify RefreshTableLinks Module in Solutions.mdb
Additional query words:
inf relink reattach reconnect refresh link attach connect ADT ODE
Keywords : kbdta PgmHowto
Version : WINDOWS:7.0,97
Platform : WINDOWS
Issue type : kbhowto
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