ACC: Procedure to Create Data Sources and Relink ODBC Tables

• Microsoft Access versions 7.0, 97

SUMMARY

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

This article shows how to create a lookup table that contains the necessary information to register an Open Database Connectivity (ODBC) Data Source Name (DSN), and create new or refresh existing ODBC tables in your application.

This article assumes that you are familiar with using the tools supplied for setting up and using ODBC Data Sources.

This article also 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

When you link a table to a Microsoft Access database using an ODBC Data Source, the information regarding that connection is stored in the Description property of the table. If you move the database to another computer that does not contain the Data Source Name (DSN) for the ODBC connection to the linked table, you receive the following error when you try to open the table:

   ODBC--connection to <ServerName> failed.

When you implement this technique in your database, you ensure that a code mechanism exists that will set up and relink to any ODBC Data Sources you use in your application.

The steps in the following example create a DSN for a SQL Server database:

1. Create a new database called TestODBC.mdb

2. Create the following table to store SQL Server ODBC Data Source information. You can modify the fields in this table to store the DSN information for any ODBC driver:

         Table: tblODBCDataSources
         -------------------------------
         Field Name: DataBase
            Data Type: Text
            Field Size: 50
         Field Name: UID
            Data Type: Text
            Field Size: 50
         Field Name: PWD
            Data Type: Text
            Field Size: 50
         Field Name: Server
            Data Type: Text
            Field Size: 50
         Field Name: ODBCTableName
            Data Type: Text
            Field Size: 50
         Field Name: LocalTableName
            Data Type: Text
            Field Size: 50
         Field Name: DSN
            Data Type: Text
            Field Size: 50
   
         Table Properties: tblODBCDataSources
         ------------------------------------
         PrimaryKey: LocalTableName
   
   

3. Create a record in the tblODBCDataSources table with information about your ODBC databases. This example uses a SQL Server connection to the Authors table in the Pubs database; substitute the correct information for your environment, and add a record for each linked table in your database:

         Field Name          Value
         -------------------------------------
         DataBase            Pubs
         UID                 sa
         PWD                 <blank>
         Server              SQLPUBS
         ODBCTableName       dbo.authors
         LocalTableName      Authors
         DSN                 Pubs
   
   

4. Create a module and type the following line in the Declarations section if it is not already there:

         Option Explicit
   

5. Type the following procedures:

         '***************************************************************
         'The DoesTblExist function validates the existence of a TableDef
         'object in the current database. The result determines if an
         'object should be appended or its Connect property refreshed.
         '***************************************************************
         Function DoesTblExist(strTblName As String) As Boolean
            On Error Resume Next
            Dim db As Database, tbl As TableDef
            Set db = CurrentDb
            Set tbl = db.TableDefs(strTblName)
            If Err.Number = 3265 Then   ' Item not found.
               DoesTblExist = False
               Exit Function
            End If
            DoesTblExist = True
         End Function
   
         Function CreateODBCLinkedTables() As Boolean
            On Error GoTo CreateODBCLinkedTables_Err
            Dim strTblName As String, strConn As String
            Dim db As Database, rs As Recordset, tbl As TableDef
            ' ---------------------------------------------
            ' Register ODBC database(s)
            ' ---------------------------------------------
            Set db = CurrentDb
            Set rs = db.OpenRecordset("tblODBCDataSources")
            With rs
               While Not .EOF
                  DBEngine.RegisterDatabase rs("DSN"), _
                           "SQL Server", _
                           True, _
                           "Description=VSS - " & rs("DataBase") & _
                           Chr(13) & "Server=" & rs("Server") & _
                           Chr(13) & "Database=" & rs("DataBase")
                  ' ---------------------------------------------
                  ' Link table
                  ' ---------------------------------------------
                  strTblName = rs("LocalTableName")
                  strConn = "ODBC;"
                  strConn = strConn & "DSN=" & rs("DSN") & ";"
                  strConn = strConn & "APP=Microsoft® Access;"
                  strConn = strConn & "DATABASE=" & rs("DataBase") & ";"
                  strConn = strConn & "UID=" & rs("UID") & ";"
                  strConn = strConn & "PWD=" & rs("PWD") & ";"
                  strConn = strConn & "TABLE=" & rs("ODBCTableName")
                  If (DoesTblExist(strTblName) = False) Then
                     Set tbl = db.CreateTableDef(strTblName, _
                                   dbAttachSavePWD, rs("ODBCTableName"), _
                                   strConn)
                     db.TableDefs.Append tbl
                  Else
                     Set tbl = db.TableDefs(strTblName)
                     tbl.Connect = strConn
                     tbl.RefreshLink
                  End If
   
                  rs.MoveNext
               Wend
            End With
            CreateODBCLinkedTables = True
            MsgBox "Refreshed ODBC Data Sources", vbInformation
         CreateODBCLinkedTables_End:
            Exit Function
         CreateODBCLinkedTables_Err:
            MsgBox Err.Description, vbCritical, "MyApp"
            Resume CreateODBCLinkedTables_End
         End Function
   
   

6. To test this function, type the following line in the Debug window, and then press ENTER:

          ?CreateODBCLinkedTables()
   

   Note that you receive the message "Refreshed ODBC Data Sources." Also note that a new linked table called Authors exists in your database, and a new User DSN called Pubs exists in the ODBC Administrator in Control Panel.

REFERENCES