Dynamically Binding Columns in Your Provider

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

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:

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    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.

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    // 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;
    }

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