PRB: RDO: CommitTrans/RollBackTrans Closes Cursor Causing Error

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

SYMPTOMS

Attempting to perform any action on an rdoResultset object connected to a SQL Server database after committing or rolling back a transaction on the rdoResultset's rdoConnection object (or simply the act of committing or rolling back the transaction), will result in the following error:

   40002
   S1010:[Microsoft][ODBC SQL Server Driver]Function sequence error

CAUSE

Depending on the cursor type, the error above will be raised either on the CommitTrans or RollBackTrans or when any attempt is made to access a property or method of the rdoResultset object after the CommitTrans or RollBackTrans.

This occurs because many servers, including SQL Server, default to closing or deleting cursors at the end of the transaction. Any action on the rdoResultset causes an action on the now-closed cursor, which causes the error. When using server-side keyset or dynamic cursors with SQL Server, RDO will erroneously call SQLExtendedFetch on the CommitTrans or RollBackTrans statement, raising this error.

RESOLUTION

While this error can be trapped and handled, the better solution is to change the connection option so that the cursors are not closed at the end of the transaction. This behavior can be changed for most servers. The code to do this with SQL Server follows. For other servers, please consult the ODBC driver and server documentation for the equivalent call.

The following code works around the problem:

1. Start a New Project.

2. Add a command button to the default form.

3. Add the following to the General Declaration section:

         Option Explicit
         'SQL Server specific connection options
          Private Const SQL_PRESERVE_CURSORS As Long = 1204
          Private Const SQL_PC_ON As Long = 1
          Private Const SQL_PC_OFF As Long = 0
   

          'Possible ODBC function returns
          Private Const SQL_ERROR As Integer = -1
          Private Const SQL_INVALID_HANDLE As Integer = -2
          Private Const SQL_NO_DATA_FOUND As Integer = 100
          Private Const SQL_SUCCESS As Integer = 0
          Private Const SQL_SUCCESS_WITH_INFO As Integer = 1
   

          Private Declare Function SQLSetConnectOption Lib "odbc32.dll" _
             (ByVal hdbc As Long, ByVal fOption As Integer, pvParam As Any) _
                 As Integer
   
          Private Declare Function SQLGetConnectOption Lib "odbc32.dll" _
             (ByVal hdbc As Long, ByVal fOption As Integer, pvParam As Any) _
                   As Integer
   
   

4. Add the following code to the click event of the CommandButton: (The server will need to be changed.)

         Private Sub Command1_Click()
          Dim intRet As Integer
          Dim lngConnOption As Long
          Dim Conn As rdoConnection
          Dim Rslt As rdoResultset
   

          'Make DSN-less connection. CHANGE SERVER UID PWD for your server
           Set Conn = rdoEnvironments(0).OpenConnection(_
               "", rdDriverComplete, False, _
          "DRIVER={SQL Server};SERVER=hoohaa;DSN=;DATABASE=pubs;UID=sa;PWD=;")
          'Getting connection option
           intRet = SQLGetConnectOption(Conn.hdbc, SQL_PRESERVE_CURSORS, _
              lngConnOption)
           If SQL_SUCCESS <> intRet Then
             MsgBox "SQLGetConnectOption Failed", "ERROR", vbCritical
             Conn.Close
            Exit Sub
          End If
          'display it
          Select Case lngConnOption
           Case SQL_PC_OFF
              MsgBox "Cursor Behavior: Close", , "Connection Option Value"
           Case SQL_PC_ON
              MsgBox "Cursor Behavior: Maintain", , "Connection Option Value"
           Case Else
             MsgBox "ERROR: Unknown Connection Option", , _
              "Connection Option Value", vbCritical
          End Select
          'uncomment the next 2 lines to stop error
        'intRet = SQLSetConnectOption(Conn.hdbc, SQL_PRESERVE_CURSORS, ByVal _
        'SQL_PC_ON)
         If intRet <> SQL_SUCCESS Then
          MsgBox "SQLSetConnectOption Failed", , "ERROR", vbCritical
          Conn.Close
          Exit Sub
         End If
         MsgBox "Connection Option Set to SQL_PC_ON", , _
            "Connection Option Status"
         Set Rslt = Conn.OpenResultset("select * from authors", _
           rdOpenDynamic, rdConcurValues)
         Conn.BeginTrans
         Rslt.MoveFirst
         Rslt.Edit
         Rslt.rdoColumns("address").Value = "test"
         Rslt.Update
         'will error on this line if connection option not set
         Conn.RollbackTrans
         Rslt.MoveLast
         Rslt.Close
         Conn.Close
        End Sub
   
   

5. Run the project and note that the code fails as indicated.

6. Uncomment the noted lines. Run the project again and note that the code does not fail.

STATUS

This behavior is not by design, but since a workaround exists, it will not be fixed.

REFERENCES

ODBC 2.0 Programmer's Guide and SDK Reference

(c) Microsoft Corporation 1998. All Rights Reserved. Contributions by Troy Cambra, Microsoft Corporation

Keywords          : vb432 VB4WIN
Version           : WINDOWS:4.0
Platform          : WINDOWS
Issue type        : kbprb