FIX: CRecordset::m_lCurrentRecord Gives Inaccurate ValuesLast reviewed: September 19, 1997Article ID: Q156135 |
The information in this article applies to:
SYMPTOMSCRecordset::m_lCurrentRecord does not correctly decrement when CRecordset::MovePrev() is invoked.
CAUSECRecordset::m_lCurrentRecord tracks the absolute position of a record within a recordset. It is modified using a value passed to the CRecordset::Move() method. The CRecordset::MovePrev() method incorrectly increments the value of m_lCurrentRecord instead of decrementing it. The source for CRecordset::MovePrev(), from Afxdb.inl, line 83-84 is shown below:
_AFXDBCORE_INLINE void CRecordset::MovePrev() { ASSERT(IsOpen()); Move(1, SQL_FETCH_PRIOR); }The value should be as follows:
_AFXDBCORE_INLINE void CRecordset::MovePrev() { ASSERT(IsOpen()); Move(-1, SQL_FETCH_PRIOR); }However, since CRecordset::MovePrev() is not virtual, it is not possible to correctly override this method.
WORKAROUNDThe solution is to override the CRecordset::SetRowsetCurrencyStatus() so that it properly decrements the m_lCurrentRecord member for a MovePrev() call. This is done in the switch statement for wFetchType == SQL_FETCH_PRIOR as shown in the sample code below.
STATUSMicrosoft has confirmed this to be a bug in the Microsoft products listed at the beginning of this article. This bug has been fixed in Visual C++ version 5.0.
MORE INFORMATIONThe use of CRecordsetStatus should be restricted to information display, and should not be relied on in a robust environment. m_lCurrentRecord is not relational, and is not be accurate in a multi-user environment. A better approach is to use bookmarks, which are more persistent. See the following methods:
CRecordset::SetBookmark() CRecordset::GetBookmark()Use of some methods may cause the bookmark to be invalidated. To determine when a bookmark is persistent and when it is not, see the following method:
CRecordset::GetBookmarkPersistence()The workaround presented below, however, ensures that CRecordset::m_lCurrentRecord is as accurate as possible.
Sample Code
extern void AFXAPI AfxSetCurrentRecord(long* plCurrentRecord, long nRows, RETCODE nRetCode); extern void AFXAPI AfxSetRecordCount(long* plRecordCount, long lCurrentRecord, long nRows, BOOL bEOFSeen, RETCODE nRetCode); void CMyRecSet::SetRowsetCurrencyStatus(RETCODE nRetCode, UWORD wFetchType, long nRows, DWORD dwRowsFetched) { // dwRowsFetched is not used, avoid warning with dummy call dwRowsFetched = 0; int nDirection; // Set the fetch direction switch (wFetchType) { case SQL_FETCH_FIRST: nDirection = 1; if (nRetCode == SQL_NO_DATA_FOUND) { m_lCurrentRecord = AFX_CURRENT_RECORD_UNDEFINED; m_lRecordCount = 0; } else m_lCurrentRecord = 0; break; case SQL_FETCH_NEXT: nDirection = 1; AfxSetCurrentRecord(&m_lCurrentRecord, nRows, nRetCode); AfxSetRecordCount(&m_lRecordCount, m_lCurrentRecord, 1, m_bEOFSeen, nRetCode); // This is the only way to know you've hit the end (m_bEOFSeen) if (!m_bEOFSeen && nRetCode == SQL_NO_DATA_FOUND && m_lRecordCount == m_lCurrentRecord + 1) m_bEOFSeen = TRUE; break; case SQL_FETCH_LAST: nDirection = -1; if (nRetCode == SQL_NO_DATA_FOUND) { m_lCurrentRecord = AFX_CURRENT_RECORD_UNDEFINED; m_lRecordCount = 0; } else if (m_bEOFSeen) m_lCurrentRecord = m_lRecordCount - 1; else m_lCurrentRecord = AFX_CURRENT_RECORD_UNDEFINED; break; case SQL_FETCH_PRIOR: nDirection = -1; AfxSetCurrentRecord(&m_lCurrentRecord, -1, nRetCode); break; case SQL_FETCH_RELATIVE: nDirection = nRows; AfxSetCurrentRecord(&m_lCurrentRecord, nRows, nRetCode); AfxSetRecordCount(&m_lRecordCount, m_lCurrentRecord, 1, m_bEOFSeen, nRetCode); break; case SQL_FETCH_ABSOLUTE: nDirection = nRows; if (nRetCode != SQL_NO_DATA_FOUND) { if (nRows > 0) m_lCurrentRecord = nRows - 1; else if (m_bEOFSeen) m_lCurrentRecord = m_lRecordCount + nRows; else m_lCurrentRecord = AFX_CURRENT_RECORD_UNDEFINED; } else m_lCurrentRecord = AFX_CURRENT_RECORD_UNDEFINED; AfxSetRecordCount(&m_lRecordCount, m_lCurrentRecord, 1, m_bEOFSeen, nRetCode); break; case SQL_FETCH_BOOKMARK: nDirection = 0; m_lCurrentRecord = AFX_CURRENT_RECORD_UNDEFINED; break; } // Set the BOF/EOF flags if (nRetCode == SQL_NO_DATA_FOUND) { if (wFetchType == SQL_FETCH_FIRST || wFetchType == SQL_FETCH_LAST || wFetchType == SQL_FETCH_BOOKMARK) { // If MoveFirst/MoveLast fails, result set is empty // If SetBookmark fails, currency undefined m_bEOF = m_bBOF = TRUE; } else { m_bEOF = nDirection >= 0 ? TRUE : FALSE; m_bBOF = !m_bEOF; } } else { m_bEOF = m_bBOF = FALSE; } } Keywords : MfcDatabase vcbuglist420 vcfixlist500 kbprg kbbuglist kbfixlist Technology : kbMfc Version : 4.2 4.2b Platform : NT WINDOWS Issue type : kbbug Solution Type : kbfix |
================================================================================
© 1998 Microsoft Corporation. All rights reserved. Terms of Use. |