Q155591: BUG: Cannot Set Access Memo Field to NULL with Snapshots

Article: Q155591
Product(s): Microsoft C Compiler
Version(s): 1.50 1.51 1.52c
Operating System(s): 
Keyword(s): kbbuglist
Last Modified: 30-AUG-2001

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The information in this article applies to:

- Microsoft Visual C++, versions 1.5, 1.51, 1.52c 
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SYMPTOMS
========

When using a Snapshot recordset with the CRecordset class, if you delete the
contents of a CString mapped to a memo field in a Microsoft Access database,
nothing is actually deleted in the database. In other words, the data that
previously existed in the field remains in that field. However, the recordset
still shows that the field has been changed to null but it has only been changed
in the cache of the cursor library, not the database.

CAUSE
=====

A problem exists in the ODBC cursor library which is used by default in MFC.

RESOLUTION
==========

This problem was resolved with the ODBC Cursor Library that ships with Visual
C++ 4.0 for 32-bit ODBC components and remains unresolved for 16-bit ODBC
components.

If possible, use dynasets in your application. If you cannot use dynasets, then
you need to replace "empty" memo fields with a single space. The code below
shows how to use this solution with a CRecordView derived class.

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.

MORE INFORMATION
================

Sample Code
-----------

The code below is from a CRecordView derived class using a recordset for an
Access data source, which has a memo field that maps to m_Memo.

      void CMyView::DoDataExchange(CDataExchange* pDX)
      {
          CRecordView::DoDataExchange(pDX);

          // Data Members --> Dialog
          if (pDX->m_bSaveAndValidate == 0)
          {
              if( m_pSet->m_Memo.GetLength() == 0 )
              {
                  m_pSet->m_Memo = " ";
              }
          }

          //{{AFX_DATA_MAP(CMyView)
          ...
          //}}AFX_DATA_MAP

          // Dialog --> Data Members
          if (pDX->m_bSaveAndValidate != 0)
          {
              if( m_pSet->m_Memo.GetLength() == 0 )
              {
                 m_pSet->m_Memo = " ";
              }
          }
      }

Additional query words: kbmfc kbdatabase kbodbc kbvc150bug kbvc151bug kbvc152bug

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Keywords          :  kbbuglist
Technology        : kbVCsearch kbAudDeveloper kbvc150 kbVC151
Version           : 1.50 1.51 1.52c

=============================================================================

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