Q201390: PRB: CDynamicAccesor Does Not Handle String Columns Correctly

Article: Q201390
Product(s): Microsoft C Compiler
Version(s): winnt:6.0
Operating System(s): 
Keyword(s): kbATL kbDatabase kbProvider kbVC600 kbGrpDSVCDB
Last Modified: 07-MAY-2001

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The information in this article applies to:

- Microsoft Visual C++, 32-bit Enterprise Edition, version 6.0 
- Microsoft Visual C++, 32-bit Professional Edition, version 6.0 
- Microsoft Visual C++, 32-bit Learning Edition, version 6.0 
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SYMPTOMS
========

If you try to update a text column using SetValue function of class
CDynamicAccessor, the column is not updated properly. Furthermore, the debug
version of your OLE DB client program may ASSERT on the following line in
ATLDBCLI.H:

  ATLASSERT(m_pColumnInfo[nColumn].ulColumnSize == sizeof(ctype));

CAUSE
=====

The SetValue function of CDynamicAccessor is a templated function to set the
value of columns of most data types. This function does not handle strings
correctly.

Following is sample code that tries to update a text column using the SetValue
function:

     void UpdateCol()
     {
        HRESULT hr;
             char szColVal[] = "Newval";
        CDataSource ds;
        CSession ses;
        hr = ds.Open("MSDASQL","Ram","sa","");
        hr = ses.Open(ds);
        CDBPropSet   propset(DBPROPSET_ROWSET);
        propset.AddProperty(DBPROP_IRowsetChange, true);
        propset.AddProperty(DBPROP_UPDATABILITY,
                                 DBPROPVAL_UP_CHANGE |
                                 DBPROPVAL_UP_INSERT |
                                 DBPROPVAL_UP_DELETE);
        CTable< CDynamicAccessor > tb;
        // Open a rowset on a table with Dynamic accessor
        hr = tb.Open(ses,"Authors",&propset);
        tb.MoveFirst();
        tb.SetValue((ULONG)1L,(char *)szColVal);
        // Call this function to set the data
        hr = tb.SetData();
     }

This code does not update the column with the given value.

RESOLUTION
==========

To avoid this problem with text columns, copy the following string directly to
the column's buffer:

   void CMultipleDlg::OnUpdate()
     {
        HRESULT hr;
        char szColVal[] = "Newval";
        CDataSource ds;
        CSession ses;
        hr = ds.Open("MSDASQL","Ram","sa","");
        hr = ses.Open(ds);
        CDBPropSet   propset(DBPROPSET_ROWSET);
        propset.AddProperty(DBPROP_IRowsetChange, true);
        propset.AddProperty(DBPROP_UPDATABILITY,
                                 DBPROPVAL_UP_CHANGE |
                                 DBPROPVAL_UP_INSERT |
                                 DBPROPVAL_UP_DELETE);
        CTable<CDynamicAccessor> tb;
        // Open a rowset on a table with Dynamic accessor
        hr = tb.Open(ses,"Authors",&propset);
        tb.MoveFirst();
        void *pName;
        // Get the address of the buffer for the second column
        pName = tb._GetDataPtr(1L);
        // copy the string to be set to the buffer
        strcpy((char *)pName,szColVal);
        // Call this function to set the data
        hr = tb.SetData();
     }

STATUS
======

This behavior is by design.

REFERENCES
==========

OLE DB template classes documentation on MSDN

Additional query words: kbDSupport

======================================================================
Keywords          : kbATL kbDatabase kbProvider kbVC600 kbGrpDSVCDB 
Technology        : kbVCsearch kbAudDeveloper kbVC600 kbVC32bitSearch
Version           : winnt:6.0
Issue type        : kbprb

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