How to use CLongBinary

[nunomas]

Hi,

We are trying to write a BLOB (LOB) column in a database via ODBC. In the RecordSet we have bound that column to a CLongBinary object but we have problems using it. After inserting a new record in the database, the field of that column appears always NULL.

Does anyone know whats the problem?

Thanks

[Chidu]

Hello,

The addition of blob field to the database needs extra care to be taken. Actually, internally when a new records is being added the Fields are set to null and the dirty flag is set byt the following functions

SetFieldNull()
SetFieldStatusDirty()

But for the blob field this is not done. So, you need to do it explicitly before the update statement.

Are you able to copy the data to CLongBinary object, if not this also has to be done explicitly by copying the data into the CLongBinary objects.

Hope this solves your problem
bye

[pav]

Don't worry!

Try CByteArray, works fine!

CByteArray d;
for(int i=0; i<size;++i)
d.SetAtGrow(i, ch[i]);

ch - source of BLOB data with length=size

[Krishnaa]

Do you have any samples for me? Please do help on how to store image into database (VC++ 5.0)

[pav]

This examples for RDBS Interbase:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

// quartzDlg.cpp : implementation file
//

#include "stdafx.h"
#include "quartzDlg.h"

void CQuartzDlg::OnStart()
{
register int i;
int transact = FALSE, failed = FALSE;

CDatabase dbase;

try
{
if(! dbase.Open(NULL, FALSE, FALSE, "ODBC;DSN=quartz;USER=dbclient;"))
return;
}
catch(CDBException *e)
{
e->ReportError();
e->Delete();
return;
}

if(dbase.CanTransact() == FALSE)
{
MessageBox("Áàçà äàííûõ íå ïîääåðæèâàåò òðàíçàêöèè","Ïðåäóïðåæäåíèå",
MB_ICONWARNING);
transact = FALSE;
}
else
{
dbase.BeginTrans();
transact = TRUE;
}

CRefer rec(&dbase);
rec.m_strFilter = _T("TYPE1ID=-1");
try
{
if(! rec.Open(CRecordset::snapshot, _T("[REFER]"),
CRecordset::executeDirect|CRecordset::appendOnly))
return;
}
catch(CDBException *e)
{
e->ReportError();
e->Delete();
return;
}


char buf[1024];
while(f.Read(buf, sizeof(buf)))
{
rec.AddNew();

// Blob ------------------------------------------------------//
for(i = 0; i < sizeof(buf); ++i) //
rec.m_SRC.SetAtGrow(i, (BYTE)(buf[i] & 0xff)); //
//
--------------------------------------------------------------//

try
{
rec.Update();
}
catch(CDBException* e)
{
e->ReportError();
e->Delete();
}
}

...

rec.Close();
dbase.Close();
}


//=========================================================================
class CRefer : public CRecordset
{
public:
CRefer(CDatabase* pDatabase = NULL);
DECLARE_DYNAMIC(CRefer)

// Field/Param Data
//{{AFX_FIELD(CRefer, CRecordset)
CByteArray m_SRC;
//}}AFX_FIELD

// Overrides
// ClassWizard generated virtual function overrides
//{{AFX_VIRTUAL(CRefer)
public:
virtual CString GetDefaultSQL(); // Default SQL for Recordset
virtual void DoFieldExchange(CFieldExchange* pFX); // RFX support
//}}AFX_VIRTUAL
};


// Refer.cpp : implementation file
//

#include "stdafx.h"
#include "Refer.h"

/////////////////////////////////////////////////////////////////////////////
// CRefer

IMPLEMENT_DYNAMIC(CRefer, CRecordset)

CRefer::CRefer(CDatabase* pdb)
: CRecordset(pdb)
{
//{{AFX_FIELD_INIT(CRefer)
m_nFields = 1;
//}}AFX_FIELD_INIT
m_nDefaultType = snapshot;
}

CString CRefer::GetDefaultSQL()
{
return _T("[REFER]");
}

void CRefer::DoFieldExchange(CFieldExchange* pFX)
{
//{{AFX_FIELD_MAP(CRefer)
pFX->SetFieldType(CFieldExchange::outputColumn);
RFX_Binary(pFX, _T("[SRC]"), m_SRC, 1024);
//}}AFX_FIELD_MAP
}