Getting BLOB fields

Hello everyone,

We have a problem with our database-access code that uses ATL.

We have a BLOB field in a SQL Server database. We access it using a
specialized accessor class. 

Later on the code look like this:
        CCommand<CAccessor<COurBLOBAccessor> >  BLOBTab;
        BLOBTab.ClearRecord();          // set all fields to 0
        BLOBTab.Open(Session);
        BLOBTab.MoveFirst();
        // use BLOBTab.m_Data to get the BLOB data

The session object is valid, the accessor gets bound properly, Open and
MoveFirst return S_OK. In a normal case, the call to MoveFirst (more
specifically, a call to IRowset::GetData) sets BLOBTab.m_Data to a valid
ISequentialStream object.

However, in one case BLOBTab.m_Data isn't set in IRowset::GetData and is
left NULL. Both IRowset::GetData and MoveFirst return S_OK but
retrieving the data is impossible.

What can be the problem?

        Michal Blazejczyk

This is how the accessor class looks like:

class COurBLOBAccessor
{
public:
        ISequentialStream* m_Data;
        ULONG m_Data_Length;
        ULONG m_Data_Status;

BEGIN_COLUMN_MAP(CSISessionBLOBAccessor)
        BLOB_ENTRY_LENGTH_STATUS(1, IID_ISequentialStream, STGM_READ,
m_Data, m_Data_Length, m_Data_Status)
        // BLOB_ENTRY_LENGTH_STATUS is our own macro. 
        // It seems to be working fine.
END_COLUMN_MAP()

        // .... Other stuff
};

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