FIX: Assertion Failure in CFieldExchange::GetColumnType()

• The Microsoft Foundation Classes (MFC) included with: - Microsoft Visual C++, 32-bit Edition, versions 2.0, 2.1, 2.2, 4.0,

       4.1, 4.2
  

SYMPTOMS

Using the MFC database classes with the Microsoft SQL Server ODBC driver versions 2.50.0121 or 2.50.0126 may cause an assertion failure after a call to SQLNumResultCols() in the CFieldExchange::GetColumnType() function.

CAUSE

This error is caused by a bug in the ODBC driver that is exposed when the cursor library is used, and happens after calling CRecordset::Requery() and then trying to edit more than one record.

The following code in Dbrfx.cpp produces the assertion:

#ifdef _DEBUG

  SWORD nResultColumns;
  AFX_SQL_ASYNC(m_prs,
                ::SQLNumResultCols(m_prs->m_hstmt, &nResultColumns));
  ASSERT(nColumn >= 1 && (long)nColumn <= (long)nResultColumns);

::SQLNumResultCols returns 0 in nResultColumns, which causes an assertion on the next line. This is due to a bug in the driver which sets the number of columns in the result set to 0. The subsequent call to ::SQLDescribeCol will also fail with SQL State S1002 "Invalid Column number" regardless of the column number specified.

RESOLUTION

To work around this problem, use a dynaset instead of a snapshot or get the 2.65.0240 version of the SQL Server driver that is included with Visual C++ 5.0.

STATUS

Microsoft has confirmed this to be a bug with the ODBC 2.5 components. This bug has been fixed in the 2.65.0240 version of the SQL Server driver that is included with Visual C++ 5.0.