FIX: CRecordset::AddNew Inserts 32484 Into int Fields (RFX_INT)

• Microsoft Visual C++, 32-bit Editions, version 5.0

SYMPTOMS

You may see one of the following problems when you update a newly-added record using a CRecordset derived class that uses RFX_Int:

• The value 32484 is saved in the table if the int data member was not modified.
• If the int data member corresponds to an identity column in the table, an error message appears indicating that an attempt was made to save a value to it. Identity fields are automatically updated by the server, and cannot be modified by external applications without setting flags on the server.
• Fields of type int that were not modified, and thus should contain NULL, contain 32484 instead. This may cause queries involving NULLs to return unexpected results.

CAUSE

This problem is caused by a bug in the RFX_Int function which always causes it to mark the int data member as dirty during AddNew. This problem occurs only if the value of the int data member was not explicitly changed.

When a record is added, all of the data members are set to pseudo null values. The application then sets the values of any members that are to be changed. Subsequently, any fields where the corresponding data member is not a pseudo null are marked as dirty and an SQL statement including all of the dirty fields is generated.

In the RFX_Int::MarkForAddNew in Visual C++ 5.0, the if clause that checks for the pseudo null value was removed. The code in 5.0 appears as follows:

   case CFieldExchange::MarkForAddNew:
   // can force writing of psuedo-null value (as a non-null) by ...
   if (!pFX->m_prs->IsFieldStatusDirty(nField - 1))
   {
      pFX->m_prs->SetDirtyFieldStatus(nField - 1);
      pFX->m_prs->ClearNullFieldStatus(nField - 1);
   }
   return;

RESOLUTION

The resolution depends on the application. The cleanest workaround is to change the int data member to a long, and use the RFX_Long function. The code problem above only exists with the int type, and most of the server data types that might be mapped to an int, such as Integer, Numeric(9), etc., will map to a long as well. This method also creates more portable code, since the size and max value of the int data type varies from one platform and operating system to another.

Another solution is to create your own RFX_Int functions. To create your own RFX_Int function, follow these steps:

1. From file vc\mfc\src\DBRFX.CPP, copy the function RFX_Int.

2. Create a new .cpp file and include the file in your project that uses ints. Place the copy of RFX_Int into this file and rename it RFX_Int1. Change the switch statement case for MarkForAddNew from the following code:

         case CFieldExchange::MarkForAddNew:
         // Can force writing of psuedo-null value (as a non-null) by
         // setting field dirty.
         if (!pFX->m_prs->IsFieldStatusDirty(nField - 1))
         {
            pFX->m_prs->SetDirtyFieldStatus(nField - 1);
            pFX->m_prs->ClearNullFieldStatus(nField - 1);
         }
         return;
   
      to:
   
         case CFieldExchange::MarkForAddNew:
         // Can force writing of psuedo-null value (as a non-null) by
         // setting field dirty.
   
         // comment out -> if (!pFX->m_prs->IsFieldStatusDirty(nField - 1))
         if (value != AFX_RFX_INT_PSEUDO_NULL)   // add in this line
         {
            pFX->m_prs->SetDirtyFieldStatus(nField - 1);
            pFX->m_prs->ClearNullFieldStatus(nField - 1);
         }
         return;
   
   

3. Include the following header information in your new project file:

         #include "stdafx.h"
   

         #ifdef AFX_DB_SEG
         #pragma code_seg(AFX_DB_SEG)
         #endif
   

         #ifdef _DEBUG
         #undef THIS_FILE
            static char THIS_FILE[] = __FILE__;
         #endif
   
         #define new DEBUG_NEW
   
   

4. Create a header file that declares your new RFX_INT1 function. Include it into any CRecordset-derived classes that need to use small integers.

5. Change all of the calls in the DoFieldExchange functions of your CRecordset-derived classes from RFX_Int to RFX_Int1.

STATUS

Microsoft 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 Studio 97 Service Pack 3.

For more information, please see the following article in the Microsoft Knowledge Base:

   ARTICLE-ID: Q170365
   TITLE     : INFO: Visual Studio 97 Service Packs - What, Where, and Why