PRB: CDynamicAccesor Does Not Handle String Columns Correctly

• Microsoft Visual C++, 32-bit Editions, version 6.0

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();
   } 

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 kbGrpVCDB
Version : winnt:6.0
Platform : winnt
Issue type : kbprb