How Do I Dynamically Bind Columns in My Provider?

Make sure you really need dynamic column binding. You may need it because:

• Your rowset columns are not defined at compile time, or

• You support an element such as bookmarks that adds columns.

To implement dynamic column binding:

• Remove any PROVIDER_COLUMN_MAPs from your code.

• In the user record (your structure), add the following declaration:

  static ATLCOLUMNINFO* _GetColumnInfo(void* pThis, ULONG* pcCols);
  

• Implement the _GetColumnInfo function. This function lays out how the information is stored. You may need to get properties or other information for this function. You may want to create a macro, similar to the COLUMN_ENTRY macro, to add your own information.

  The following example shows a _GetColumnInfo function.

  // Check the property flag for bookmarks, if it is set, set the zero
  // ordinal entry in the column map with the bookmark information.
  CAgentRowset* pRowset = (CAgentRowset*) pThis;
  CComQIPtr<IRowsetInfo, &IID_IRowsetInfo> spRowsetProps = pRowset;
  
  CDBPropIDSet set(DBPROPSET_ROWSET);
  set.AddPropertyID(DBPROP_BOOKMARKS);
  DBPROPSET* pPropSet = NULL;
  ULONG ulPropSet = 0;
  HRESULT hr;
  
  if (spRowsetProps)
  hr = spRowsetProps->GetProperties(1, &set, &ulPropSet, &pPropSet);
  
  if (pPropSet)
  {
  CComVariant var = pPropSet->rgProperties[0].vValue;
  CoTaskMemFree(pPropSet->rgProperties);
  CoTaskMemFree(pPropSet);
  
  if (SUCCEEDED(hr) && (var.boolVal == VARIANT_TRUE))
  {
  ADD_COLUMN_ENTRY_EX(ulCols, OLESTR("Bookmark"), 0, sizeof(DWORD), DBTYPE_BYTES,
  0, 0, GUID_NULL, CAgentMan, dwBookmark, DBCOLUMNFLAGS_ISBOOKMARK)
  ulCols++;
  }
  }
  
  // Next set the other columns up.
  ADD_COLUMN_ENTRY(ulCols, OLESTR("Command"), 1, 256, DBTYPE_STR, 0xFF, 0xFF,
  GUID_NULL, CAgentMan, szCommand)
  ulCols++;
  ADD_COLUMN_ENTRY(ulCols, OLESTR("Text"), 2, 256, DBTYPE_STR, 0xFF, 0xFF,
  GUID_NULL, CAgentMan, szText)
  ulCols++;
  
  ADD_COLUMN_ENTRY(ulCols, OLESTR("Command2"), 3, 256, DBTYPE_STR, 0xFF, 0xFF,
  GUID_NULL, CAgentMan, szCommand2)
  ulCols++;
  ADD_COLUMN_ENTRY(ulCols, OLESTR("Text2"), 4, 256, DBTYPE_STR, 0xFF, 0xFF,
  GUID_NULL, CAgentMan, szText2)
  ulCols++;
  
  
  if (pcCols != NULL)
  *pcCols = ulCols;
  
  return _rgColumns;
  }