Re: Getting BLOB fields

Hi,

What do you mean, "parametrized statement"? As far as I can see, there's
only one accessor, it retrieves two fields: ID and Data.
And this works in ALMOST ALL cases. We've never encountered this kind of
problem before.
What might help is that the guy who sent us this database file (ooops,
made a mistake below: this is MS Access, not SQL Server!) had a problem
with the database, it was corrupted or something (he was getting weird
errors while trying to open the database file in MS Access).

Regards

        Michal

> -----Original Message-----
> From: Yuancai Ye [mailto:[email protected]]
> Sent: Friday, May 10, 2002 13:35
> To: [email protected]
> Subject: Re: [OLEDB_DEV] Getting BLOB fields
> 
> 
> Hi,
>    You use a parameterized statement to retrieve a
> rowset. If so, two accessors are involved at least. I
> usually use OleDBPro instead of ATL consumer
> templates. If you like, see the samples BLOBs and
> AOTBLOB inside the OleDBPro module.
> 
> Yuancai (Charlie) Ye
> See 30 real well-tested advanced OLEDB samples
> Use of free SocketPro for creating super client and
> server application with numerous samples
> www.udaparts.com
> 
> --- Michal Blazejczyk
> <[email protected]> wrote:
> > Hi,
> >
> > This is not the case since we retrieve only one
> > record at a time. We use
> > the following command in our accessor: "SELECT Data
> > FROM Session WHERE
> > (ID=?)". Of course, the accessor also contains a
> > LONG m_ID field
> > mapped properly.
> >
> > Regards
> >
> >         Michal
> >
> >
> > > -----Original Message-----
> > > From: Yuancai Ye [mailto:[email protected]]
> > > Sent: Friday, May 10, 2002 13:15
> > > To: [email protected]
> > > Subject: Re: [OLEDB_DEV] Getting BLOB fields
> > >
> > >
> > > Hi,
> > >    Did you release the BLOB object after
> > retrieving a
> > > BLOB before moving to the next record?
> > >
> > > Yuancai (Charlie) Ye
> > > See 30 real well-tested advanced OLEDB samples
> > > Use of free SocketPro for creating super client
> > and
> > > server application with numerous samples
> > > www.udaparts.com
> > >
> > > --- Michal Blazejczyk
> > > <[email protected]> wrote:
> > > > 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
> > > > };
> > > >
> > > > You can read messages from the OLEDB_DEV
> > archive,
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> > >
> > >
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