PRB: RDO Forward-Only Cursor Doesn't Allow MoveLast

• Enterprise Edition of Microsoft Visual Basic for Windows, 32-bit only, version 4.0

SYMPTOMS

If you try to use the MoveLast method on a forward-only remote data object recordset, you receive the error

   "S1106: [Microsoft][ODBC SQL Server Driver]Fetch type out of range".

CAUSE

Forward-only cursors only allow the use of MoveNext methods. This is a limitation of ODBC.

RESOLUTION

There is no direct way to implement an exact copy of MoveLast with code when using a resultset with a forward-only cursor. The following code loops through and touches all records in a resultset. When the loop finishes, the current record will be the EOF marker.

   'The following code loops through all the records in a resultset
   While Not rdoToMove.EOF
      'do any processing here
      rdoToMove.MoveNext
   Wend

STATUS

This behavior is by design.

MORE INFORMATION

When RDO works with a forward-only resultset, it uses a call to the ODBC API function SQLExtendedFetch to obtain data. As one of its parameters, this function takes a value that specifies the type of fetch to be performed. ODBC specifies that when a resultset has a forward-only cursor, this fetch argument may only be SQL_FETCH_NEXT. If the argument is something besides this constant, ODBC returns 'S1106: Fetch type out of range,' indicating that the argument was invalid. For more information, see the reference listed in the References section below.

Steps to Reproduce

1. Start Visual Basic.

2. On the File menu, click New Project.

3. Double-click the Command button icon in the Toolbox to create a command button on the form.

4. Insert the following code in the command button's Click event. Replace strDSN, strConnect, and strSQL with the relevant values for your database.

      Private Sub Command1_Click()
                Dim ps As rdoPreparedStatement
                Dim conn As rdoConnection
                Dim strDSN As String
                Dim strConnect As String
                Dim strSQL As String
   
                strDSN = "pubs"
                strConnect = "uid=sa;pwd=;database=pubs"
                strSQL = "Select * From Authors"
   
   
                With rdoEnvironments(0)
                    .CursorDriver = rdUseOdbc
                Set conn = .OpenConnection _
                  (strDSN, rdDriverNoPrompt, False, strConnect)
                End With
                Set ps = conn.CreatePreparedStatement("", strSQL)
                Set rs = ps.OpenResultset(rdOpenForwardOnly)
   
                rs.MoveLast      'this line causes the error
   
      End Sub
   
   

5. On the Run menu, click Start (ALT, R, S) or press the F5 key. The program will stop when it reaches the rs.Movelast line, and give the error listed above.

REFERENCES

Microsoft ODBC 2.0 Programmer's Reference and SDK Guide: SQLExtendedFetch function - return code S1106.