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The CDynamicAccesor class does not handle string columns correctly in Visual C++

Article ID: 201390

Article Last Modified on 1/9/2006

Microsoft Visual C++ 2005 Express Edition
Microsoft Visual C++ .NET 2003 Standard Edition
Microsoft Visual C++ .NET 2002 Standard Edition
Microsoft Visual C++ 6.0 Enterprise Edition
Microsoft Visual C++ 6.0 Professional Edition
Microsoft Visual C++ 6.0 Standard Edition

This article was previously published under Q201390

SYMPTOMS

If you try to update a text column using SetValue function of the CDynamicAccessor class, the column is not updated correctly. 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 the CDynamicAccessor class 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

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