Dynamically Binding Columns in Your Provider

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

• Your rowset columns aren't defined at compile time.

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

To implement dynamic column binding

1. Remove any PROVIDER_COLUMN_MAPs from your code.

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

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

3. Implement the GetColumnInfo function. This function lays out how the information is stored. You might need to get properties or other information for this function. You might 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 up the other columns.
   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;
   }
   

See also

Working with OLE DB Provider Templates