Q152318: FIX: DAO SDK’s CdbRecordset::Requery() May Fail

Article: Q152318
Product(s): Microsoft C Compiler
Version(s): 4.0 4.1
Operating System(s): 
Keyword(s): kbProgramming
Last Modified: 04-AUG-2001

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

- The DAO SDK, included with:
   - Microsoft Visual C++, 32-bit Editions, versions 4.0, 4.1 
-------------------------------------------------------------------------------

SYMPTOMS
========

Attempting to invoke the DAO SDK's CdbRecordset::Requery() method of the
CdbRecordset class when the recordset has been opened with dbOpenDynaset and
dbDenyWrite, may result in an error message similar to the following:

  

  Unhandled exception in <YourApp>.exe (DAO3032.DLL):
  0xC0000005: Access Violation

CAUSE
=====

Within the implementation of CdbRecordset::Requery found in DBDAO.CPP (line
1645), the casting of a COleVariant method is performed incorrectly. The cast is
performed as:

     Var.pdispVal    = (LPDISPATCH)pq();

The correct implementation should be:

     Var.pdispVal    = (LPDISPATCH)pq->GetInterface();

RESOLUTION
==========

Derive a new class from CdbRecordset and override the Requery method with the
following:

     VOID CdbRecordset::Requery( CdbQueryDef *pq )   // = NULL
     {
         DAORecordset*   prs = (DAORecordset *)GetInterface();
         COleVariant     Var;

         //Manually load the Query Def as a dispatch
         if (!pq)
         {
             Var.vt          = VT_ERROR;
             Var.scode       = DISP_E_PARAMNOTFOUND;
         }
         else
         {
             Var.vt          = VT_DISPATCH;
             Var.pdispVal    = (LPDISPATCH)pq->GetInterface();
         }

         DAOMFC_CALL(prs->Requery(Var));
     }

STATUS
======

Microsoft has confirmed this to be a bug in the Microsoft products listed at the
beginning of this article. This bug was corrected in fixed in the DAO SDK that
comes with Visual C++ version 5.0.

Additional query words:

======================================================================
Keywords          : kbProgramming 
Technology        : kbAudDeveloper kbDAOsearch kbSDKDAOSearch kbSDKSearch
Version           : 4.0 4.1
Issue type        : kbbug
Solution Type     : kbfix

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

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