BUG: CRecordset Does Not Set HSTMT Attributes for Updates

• The Microsoft Foundation Classes (MFC)
• Microsoft Visual C++, 32-bit Enterprise Edition, versions 5.0, 5.0sp1, 5.0sp2, 5.0sp3

SYMPTOMS

When updating using the cursor library or when using a cursor that causes MFC to use SQL statements to update, CRecordset errors can occur when using strings containing ODBC escape sequences. For example, the string “{d2fcfefb-6126-11d1-84c1-0020afd6c52f}” may cause a data conversion error because “{d” is the ODBC escape sequence for a date. The error occurs whether the SQLSetStmtOption() attribute SQL_NOSCAN is set to SQL_NOSCAN_ON or SQL_NOSCAN_OFF.

CAUSE

In the CRecordset::PrepareUpdateHstmt() function, CRecordset allocates a handle to use to update m_hstmtUpdate. However, CRecordset does not apply the HSTMT attributes on its default HSTMT, m_hstmt, to m_hstmtUpdate. Therefore any statement attributes set by the user will not be seen in an update.

For example, given the code:

   void CSampleSet::OnSetOptions(HSTMT hstmt)
   {
      CRecordset::OnSetOptions(hstmt);

      SQLSetStmtOption(hstmt, SQL_NOSCAN, SQL_NOSCAN_ON);
   }

RESOLUTION

It is possible to work around this bug by taking the following steps:

For dynamically linking the MFC library:

1. Copy the implementations of CRecordset::UpdateInsertDelete() and CRecordset::PrepareUpdateHstmt() to your CRecordset derived class.

2. If you haven't already implemented the virtual CRecordset::Update() function, copy the MFC implementation of that method.

3. In the copied CRecordset::PrepareUpdateHstmt(), change the block of code that reads

         if (m_hstmtUpdate == SQL_NULL_HSTMT)
         {
            AFX_SQL_SYNC(::SQLAllocStmt(m_pDatabase->m_hdbc, &m_hstmtUpdate));
            if (!Check(nRetCode))
            {
               TRACE0("Error: failure to allocate update statement.\n");
               AfxThrowDBException(nRetCode, m_pDatabase, m_hstmtUpdate);
            }
         }
   
      to the following:
   
         if (m_hstmtUpdate == SQL_NULL_HSTMT)
         {
            AFX_SQL_SYNC(::SQLAllocStmt(m_pDatabase->m_hdbc, &m_hstmtUpdate));
            if (!Check(nRetCode))
            {
               TRACE0("Error: failure to allocate update statement.\n");
               AfxThrowDBException(nRetCode, m_pDatabase, m_hstmtUpdate);
            }
   
            OnSetOptions(m_hstmtUpdate);
         }
   
   

For statically linking the MFC library, you can either follow the steps above or you can modify your version of MFC sources directly by following step 3 above in the CRecordset class and rebuilding.

It is highly recommended that developers do not directly modify the MFC source. For more information on rebuilding the MFC static library, see the README.TXT file in the MFC\SRC directory.

STATUS

Microsoft has confirmed this to be a bug in the Microsoft products listed at the beginning of this article. We are researching this bug and will post new information here in the Microsoft Knowledge Base as it becomes available.

REFERENCES

For more information on ODBC escape sequences, see Chapter 8 and Appendix C, ODBC Programmers Reference.