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CMyProviderRowset (MyProviderRS.H)

 

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The latest version of this topic can be found at CMyProviderRowset (MyProviderRS.H).

The wizard generates an entry for the rowset object. In this case, it is called CMyProviderRowset. The CMyProviderRowset class inherits from an OLE DB provider class called CRowsetImpl, which implements all the necessary interfaces for the rowset object. The following code shows the inheritance chain for CRowsetImpl:

template <class T, class Storage, class CreatorClass,   
   class ArrayType = CAtlArray<Storage> >  
class CMyRowsetImpl:  
   public CRowsetImpl<T, Storage, CreatorClass, ArrayType,   
      CSimpleRow, IRowsetLocateImpl< T > >  

CRowsetImpl also uses the IAccessor and IColumnsInfo interfaces. It uses these interfaces for output fields in tables. The class also provides an implementation for IRowsetIdentity, which allows the consumer to determine if two rows are identical. The IRowsetInfo interface implements properties for the rowset object. The IConvertType interface allows the provider to resolve differences between data types requested by the consumer and those used by the provider.

The IRowset interface actually handles data retrieval. The consumer first calls a method called GetNextRows to return a handle to a row, known as an HROW. The consumer then calls IRowset::GetData with that HROW to retrieve the requested data.

CRowsetImpl also takes several template parameters. These parameters allow you to determine how the CRowsetImpl class handles data. The ArrayType argument allows you to determine what storage mechanism is used to store the row data. The RowClass parameter specifies what class contains an HROW.

The RowsetInterface parameter allows you to also use the IRowsetLocate or IRowsetScroll interface. The IRowsetLocate and IRowsetScroll interfaces both inherit from IRowset. Therefore, the OLE DB provider templates must provide special handling for these interfaces. If you want to use either of these interfaces, you need to use this parameter.

Provider Wizard-Generated Files

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