Q130956: PRB: MFC DB Classes Don’t Update NULL Field Values to Non-NULL

Article: Q130956
Product(s): Microsoft C Compiler
Version(s): winnt:
Operating System(s): 
Keyword(s): kbcode kbDatabase kbMFC kbODBC kbVC kbprb
Last Modified: 25-JUL-2001

-------------------------------------------------------------------------------
The information in this article applies to:

- The Microsoft Foundation Classes (MFC), used with:
   - *EDITOR Please do not choose this product*Microsoft Visual C++ 32-bit Edition* use 241, 265, 225, version 2.0 
-------------------------------------------------------------------------------

SYMPTOMS
========

When the MFC Database classes that come with Visual C++ version 2.0 are used,
any field that has a NULL value cannot be updated to a non-NULL value
successfully.

After opening a recordset on a SQL Server table that has fields with NULL values,
the Edit() and Update() methods of the recordset fail to update the value of the
field to a non-NULL value. For example, the following code isn't able to do the
update:

     CMyRecordSet rs;
     rs.Open();
     rs.Edit();
     rs.m_Name="Test"; //m_Name allows NULLs and is NULL for current record
     rs.Update();

The Update() function doesn't return any error, but the m_Name value is still set
to NULL.

RESOLUTION
==========

Use the MFC Database Classes that come with Visual C++ version 2.1 or above.
Otherwise, for the field to be updated, force the bNull flag of the
SetFieldNull() method to FALSE before calling the Update(). The following code
works:

     CMyRecordSet rs;
     rs.Open();
     rs.Edit();
     rs.m_Name="Test";  //m_Name allows NULLs and is NULL for current record
     rs.SetFieldNull(&rs.m_Name, FALSE);
     rs.Update();

STATUS
======

This behavior is by design.

Additional query words: 2.00 3.00 ODBC

======================================================================
Keywords          : kbcode kbDatabase kbMFC kbODBC kbVC kbprb 
Technology        : kbAudDeveloper kbMFC
Version           : winnt:
Issue type        : kbprb

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

THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND. MICROSOFT DISCLAIMS ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL, CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. SOME STATES DO NOT ALLOW THE EXCLUSION OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES SO THE FOREGOING LIMITATION MAY NOT APPLY.

Copyright Microsoft Corporation 1986-2002.