Modifying the Inheritance of RMyProviderRowset
The latest version of this topic can be found at Modifying the Inheritance of RMyProviderRowset.
To add the IRowsetLocate interface to the simple read-only provider example, modify the inheritance of RMyProviderRowset. Initially, RMyProviderRowset inherits from CRowsetImpl. You need to modify it to inherit from CRowsetBaseImpl.
To do this, create a new class, CMyRowsetImpl, in MyProviderRS.h:
////////////////////////////////////////////////////////////////////////
// MyProviderRS.h
template <class T, class Storage, class CreatorClass, class ArrayType = CAtlArray<Storage> >
class CMyRowsetImpl:
public CRowsetImpl<T, Storage, CreatorClass, ArrayType, CSimpleRow, IRowsetLocateImpl< T, IRowsetLocate > >
{
...
};
Now, edit the COM interface map in MyProviderRS.h to be as follows:
BEGIN_COM_MAP
(CMyRowsetImpl)
COM_INTERFACE_ENTRY
(IRowsetLocate)
COM_INTERFACE_ENTRY_CHAIN
(_RowsetBaseClass)
END_COM_MAP
()
This creates a COM interface map that tells CMyRowsetImpl to call QueryInterface for both the IRowset and IRowsetLocate interfaces. To get all of the implementation for the other rowset classes, the map links the CMyRowsetImpl class back to the CRowsetBaseImpl class defined by the OLE DB Templates; the map uses the COM_INTERFACE_ENTRY_CHAIN macro, which tells OLE DB templates to scan the COM map in CRowsetBaseImpl in response to a QueryInterface call.
Finally, link RAgentRowset to CMyRowsetBaseImpl by modifying RAgentRowset to inherit from CMyRowsetImpl, as follows:
class RAgentRowset : public CMyRowsetImpl<RAgentRowset, CAgentMan, CMyProviderCommand>
RAgentRowset can now use the IRowsetLocate interface while taking advantage of the rest of the implementation for the rowset class.
When this is done, you can dynamically determine columns returned to the consumer.