Re: Getting BLOB fields

Hi,

As far as I can figure out the code (I didn't write it), the '?' char
stands for 'will be replaced on runtime by the value of the ID field of
the accessor object'. The '?' appears in the code itself, NOT on
runtime. I guess that's how ATL works.

Regards

        Michal

> -----Original Message-----
> From: Yuancai Ye [mailto:[email protected]]
> Sent: Friday, May 10, 2002 13:47
> To: [email protected]
> Subject: Re: [OLEDB_DEV] Getting BLOB fields
> 
> 
> Hi, Michal:
>    I saw the char '?' with your SQL statement in your
> previous message. So you want to open a corrupted
> Access file. Maybe the corrupted access file leads to
> this problem.
> 
> 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,
> >
> > 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,
> > > > > > unsubscribe from OLEDB_DEV,
> > > > > > or subscribe to other DevelopMentor lists at
> > > > > http://discuss.develop.com.
> > > > >
> > > > >
> > > > >
> > __________________________________________________
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> 
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