Microsoft KB Archive/209862

= How to relink back-end tables with the common dialog control in Access 2000 =

Article ID: 209862

Article Last Modified on 6/23/2005

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APPLIES TO


 * Microsoft Access 2000 Standard Edition

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This article was previously published under Q209862





For a Microsoft Access 97 version of this article, see 181076.

Advanced: Requires expert coding, interoperability, and multiuser skills.

This article applies only to a Microsoft Access database (.mdb).



SUMMARY
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 Microsoft Office 2000 Developer Edition Tools. 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 Microsoft Windows application programming interface (API) functions, refer to the Developer Solutions sample program (Solutions9.mdb.) To obtain Solutions9.mdb, click the article number below to view the article in the Microsoft Knowledge Base:

248674 ACC2000: Orders and Developer Solutions Sample Databases Available on the Microsoft Developer Network (MSDN)

Open the Solutions9.mdb database, select Use multiple databases in the Select a Category of Examples box, and then click Link tables at startup in the Select an Example box.



MORE INFORMATION
Microsoft provides programming examples for illustration only, without warranty either expressed or implied. This includes, but is not limited to, the implied warranties of merchantability or fitness for a particular purpose. This article assumes that you are familiar with the programming language that is being demonstrated and with the tools that are used to create and to debug procedures. Microsoft support engineers can help explain the functionality of a particular procedure, but they will not modify these examples to provide added functionality or construct procedures to meet your specific requirements. A program that uses split database design has its tables in one database in a shared network location (the back-end database), and all of 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 program. You can enable your program 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 shows you how to relink table data in your program. This method uses a form that a user can open to relink the back-end tables, and another optional form that can automatically verify the back-end link when the database is opened.

This article assumes that you have the Microsoft Common Dialog control, which is available with Microsoft Office 2000 Developer Edition Tools. 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 program, you must use the Package and Deployment Wizard to include the Common Dialog Control file, Comdlg32.ocx, and its supporting DLLs with your setup files. For more information about using the Package and Deployment Wizard, see the articles listed in the "References" section of this article.

Method to Relink Back-End Database Tables
CAUTION: If you follow the steps in this example, you modify the sample database Northwind.mdb. You may want to back up the Northwind.mdb file and follow these steps on a copy of the database.

 Create a new blank Access database file and name it FrontEnd.mdb . On the File menu, point to Get External Data, and then click Link Tables. Browse to select the sample database Northwind.mdb, and then click Link. In the Link Tables dialog box, click Select All, and then click OK. 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...

On Click: =Browse

Command button:

Name: cmdLinkNew

Caption: Refresh Links

On Click: =Processtables

Command button:

Name: cmdCancel

Caption: Cancel

OnClick: [Event Procedure]

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" DoCmd.Close acForm, Me.Name

Exit_cmdCancel_Click: Exit Sub

Err_cmdCancel_Click: MsgBox Err.Description Resume Exit_cmdCancel_Click

End Sub </li> On the Debug menu, click Compile FrontEnd.</li> Save the frmNewDataFile form and close it.</li> In the Database window, click Modules, and then click New.</li> On the Tools menu, click References, select Microsoft DAO 3.6 Object Library if it is not already selected, and then click OK.</li>  Type or paste the following code: Dim UnProcessed As New Collection 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 Len(.FileName) > 0 Then ' user responded, put selection into text box on form. [Forms]![frmNewDatafile]![txtFileName] = .FileName End If   End With

Exit_Browse: Exit Function

Err_Browse: MsgBox Err.Description Resume Exit_Browse

End Function

Public Sub AppendTables

Dim db As DAO.Database, x As Variant Dim strTest As String ' Add names of all table with invalid links to the Unprocessed Collection. Set db = CurrentDb ClearAll For Each x In db.TableDefs If Len(x.Connect) > 1 And Len(Dir(Mid(x.Connect, 11))) = 0 Then ' connect string exists, but file does not 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 tables with broken links 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.Number & ": " & 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 DAO.Database, dblocal As DAO.Database, ws As Workspace, x, y   Dim tdlocal As DAO.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.Number & ": " & 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.Number & ": " & Err.Description Resume Exit_BeginLink

End Sub </li> On the Debug menu, click Compile FrontEnd.</li> Save the module as RelinkCode, and then close it.</li> Rename the Northwind.mdb sample database or move it to another folder on your hard disk so that the linked tables in FrontEnd.mdb will need to be refreshed.</li> Open the frmNewDataFile form, and then 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 finished:

Linking to new back-end data file was successful.

</li></ol>

Creating a Startup Form to Check Linked Tables
To verify the links to back-end tables automatically each time that you open the FrontEnd.mdb database, you can create a hidden form for that purpose by following these steps: <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 run 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 DAO.Database Dim td As DAO.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. DoCmd.Close acForm, Me.Name Exit Sub                         ' to refresh links 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 Err.Number & ": " & Error.Description Resume Exit_Form_Open End Sub </li> On the Debug menu, click Compile FrontEnd.</li> <li>Save the form as frmCheckLink, and then close it.</li> <li>To set frmCheckLink as the startup form, on the Tools menu click Startup, select frmCheckLink in the Display Form/Page list, and then click OK.</li> <li>To make frmCheckLink a hidden form, right-click frmCheckLink in the Database window, click Properties on the shortcut menu, click to select 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 disk so that the linked tables in FrontEnd.mdb will need to be refreshed.</li> <li>Close and then reopen FrontEnd.mdb.

Notice that you receive the following error message

Can't find the back-end file. Please choose new data file.

where  is the path and file name of your back-end database.

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 the following error message:

The linked tables can't find their source. Please log onto network and restart the program.

</li></ol>

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