Microsoft KB Archive/181076

= ACC: How to Relink Back-End Tables with Common Dialog Control =

Article ID: 181076

Article Last Modified on 1/22/2007

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APPLIES TO


 * Microsoft Access 95 Standard Edition
 * Microsoft Access 97 Standard Edition

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This article was previously published under Q181076





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").</li> Save the frmNewDataFile form and close it.</li> In the Database Window, click the Modules tab,</li>  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 </li> 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").</li> Save the module as RelinkCode and close it.</li> 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.</li> Open the frmNewDataFile form, and click the Browse button.</li> 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.</li> 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.

</li></ol>

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: <ol> Create a new form not based on any table or query in Design view.</li> On the View menu, click Code.</li>  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 </li> 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").</li> Save the form as frmCheckLink, and then close it.</li> 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.</li> <li>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.</li> <li>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.</li> <li>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.

</li></ol>

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