Re: Getting BLOB fields

Hi,
   What version of VC++ are you using? 7 or 6. I get
confused. Believe me. If it is a parameterized
statement, you must use two accessors at least. If
your statement is just a simple SQL query, one
accessor is fine in most cases.

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,
>
> 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;
>
=== message truncated ===


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