How to refresh links in a runtime application in Microsoft Access

Summary

In a run-time application, the front-end and back-end databases must be stored in the same folder. Even though you can change the default installation path of the back-end database to, for example, $AppPath\Folder1, there is no way for Access to refresh the links in the front-end to match the new installation location.

One way to work around this behavior is to programmatically refresh the links by using ActiveX Extensibility Objects (ADOX) after the run-time application has been installed. The following is an illustration of how to implement this technique. Please note that this article assumes that the back-end databases are stored in subfolders under the front-end database.

More Information

  1. Make sure you have the latest version of the Microsoft Data Access Components (MDAC) installed on your computer. MDAC can be found at the following Microsoft Web site:
  2. Set a reference to Microsoft ADO Ext 2.5 (or later) for DDL and Security.
  3. Create a new database and name it FrontEnd.mdb.
  4. Import the Customers and Employees forms from the sample database Northwind.mdb into FrontEnd.mdb.
  5. Create a new database and subfolder under the folder where the FrontEnd.mdb file is located, for example, Folder1\Backend1.mdb.
  6. Import the Customer table from Northwind.mdb into Backend1.mdb.
  7. Create a new database and subfolder under the folder where the FrontEnd.mdb file is located, for example, Folder2\Backend2.mdb.
  8. Import the Employee table from Northwind.mdb into Backend2.mdb.
  9. Open the FrontEnd.mdb database and create a new module. In the module, paste in the following code:
    Option Compare Database
    Option Explicit

    Private Declare Function apiSearchTreeForFile Lib "ImageHlp.dll" Alias _
    "SearchTreeForFile" (ByVal lpRoot As String, ByVal lpInPath _
    As String, ByVal lpOutPath As String) As Long


    Function RefreshLinks()
    On Error GoTo ErrorHandler


    Dim objCat As New ADOX.Catalog 'Define the ADOX Catalog Object
    Dim objTbl As ADOX.Table 'Define the ADOX Table Object

    Dim strSearchFolder As String 'Folder to Search in.
    Dim strFilename As String 'Db Name of the Linked Table
    Dim strFullName As String 'Path & DB Name of the Linked Table.
    Dim strSearchFile As String 'The new path of the database.

    Dim blnTablesNotLinked As Boolean 'Determines if links are valid

    'Open the catalog
    objCat.ActiveConnection = CurrentProject.Connection

    'Loop through the table collection and refresh the linked tables.
    For Each objTbl In objCat.Tables

    ' Check to make sure the table is a linked table.
    If objTbl.Type = "LINK" Then
    strFullName = objTbl.Properties("Jet OLEDB:Link Datasource")
    strFilename = Mid(strFullName, InStrRev(strFullName, "\", _
    Len(strFullName)) + 1, Len(strFullName))
    strSearchFolder = CurrentProject.Path
    'The following line of code attempts to refresh the link.
    'If the source cannot be found an error is generated.
    'Please note that this code only checks one table to determine
    'whether or not the links are valid.
    objTbl.Properties("Jet OLEDB:Link Datasource") = strFullName

    If blnTablesNotLinked = False Then
    Exit Function
    Else
    'Set the search path to the path of the current project.
    'The assumption is that the linked tables are located in subfolders.
    strSearchFile = SearchFile(strFilename, strSearchFolder)
    objTbl.Properties("Jet OLEDB:Link Datasource") = strSearchFile
    End If
    End If
    Next

    MsgBox "The links were successfully refreshed!!! "

    ExitHandler:
    Exit Function

    ErrorHandler:
    Select Case Err.Number
    Case -2147467259
    blnTablesNotLinked = True
    Resume Next
    Case Else
    MsgBox Err.Description & " " & Err.Number
    Resume ExitHandler
    End Select
    End Function

    Function SearchFile(ByVal strFilename As String, _
    ByVal strSearchPath As String) As String
    'Search the folder for first occurrence of the source databases.
    Dim strBuffer As String
    Dim lngResult As Long
    SearchFile = ""
    strBuffer = String$(1024, 0)
    lngResult = apiSearchTreeForFile(strSearchPath, strFilename, strBuffer)
    If lngResult <> 0 Then
    If InStr(strBuffer, vbNullChar) > 0 Then
    SearchFile = Left$(strBuffer, InStr(strBuffer, vbNullChar) - 1)
    End If
    End If
    End Function
    This function checks the first linked table in the database to determine if the links are valid. If the links are not valid, the function searches for the database and refreshes the links.
  10. Create a new macro with the following properties, and name it AutoExec:

    Action: RunCode
    Function Name: RefreshLinks()

    Action: OpenForm
    Form Name: Customers

    Action: OpenForm
    Form Name: Employees
    Note that you can also call this function in the Open event of a hidden Startup Form.
  11. Build the package for the run-time application. Remember to add "Folder1" and "Folder2" to the respective installation locations.

    For Access 2007 and for Access 2003, add the back-end files in the "Additional Files" section, and then provide respective folder names "Folder1" and "Folder2" in the Install Subfolder column.

    For Access 2002 and for Access 2000, add "$(AppPath)\Folder1\" and "$(AppPath)\Folder2\" to the respective installation locations on the Install Location page.

  12. Deploy the run-time application.
When the application starts, an hourglass indicates that the links are being refreshed. The Customers and Employees forms will then open with valid data.

References

For more information about how to refresh linked tables, click the following article number to view the article in the Microsoft Knowledge Base:

209862 How to relink back-end tables with the common dialog control in Access 2000

Properties

Article ID: 291264 - Last Review: Oct 30, 2008 - Revision: 1

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