BLOB Field

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2 total messages Started by kev Tue, 07 Feb 2006 18:03

#660

Author: kev
Date: Tue, 07 Feb 2006 18:03

36 lines
2178 bytes

I am having a difficult time writing "BLOB" data into a SQL Server database.
I can read the data out with no problem using the following code:

        MemSize = Field1->DataSize; // add one for null terminator
        ByteBuffer = new byte[MemSize]; // Allocate the memory.
        TempBuffer = new byte[MemSize]; // Allocate the memory.

        Field1->GetData(ByteBuffer,true);

A call to IsBlob() returns False so I have to use GetData();  The database
field is defined as VarBinary, Max=7800, allow nulls = no and key = no.  At
any rate the returned data is fine.

This all works fine, however...

Now I want to modify the data, create a new record and write the "blob" back
into the database.  All I can see seem to get is a record with the blob
field empty.  I have tried many different things with only 1 successful
attempt.  The problem is I don't know exactly the steps I used for that one.
Here is a sample of what I am trying:

TField * Field1 =
(TField*)CalibrationTemplates->FieldByName("TemplateData");
Templates->Append();  //TADODataSet
// Write the Modified data bact to a new record.
// ModBuffer is defined as shown above
Field1->SetData(ModBuffer,true);
Templates->UpdateRecord();

I populate other fields using FieldByName->AsString etc.  The new record
sometimes will show up in the database, but the TemplateData is empty.

Any ideas?

thanks,
Kev

Re: BLOB Field

#661

Author: Arnie
Date: Tue, 07 Feb 2006 20:15

84 lines
3472 bytes

"kev" <kev@isp.com> wrote in message 
news:43e8e007$1@newsgroups.borland.com...
>I am having a difficult time writing "BLOB" data into a SQL 
>Server database.
> I can read the data out with no problem using the following 
> code:
>
>        MemSize = Field1->DataSize; // add one for null 
> terminator
>        ByteBuffer = new byte[MemSize]; // Allocate the memory.
>        TempBuffer = new byte[MemSize]; // Allocate the memory.
>
>        Field1->GetData(ByteBuffer,true);
>
> A call to IsBlob() returns False so I have to use GetData(); 
> The database
> field is defined as VarBinary, Max=7800, allow nulls = no and 
> key = no.  At
> any rate the returned data is fine.
>
> This all works fine, however...
>
> Now I want to modify the data, create a new record and write 
> the "blob" back
> into the database.  All I can see seem to get is a record with 
> the blob
> field empty.  I have tried many different things with only 1 
> successful
> attempt.  The problem is I don't know exactly the steps I used 
> for that one.
> Here is a sample of what I am trying:
>
> TField * Field1 =
> (TField*)CalibrationTemplates->FieldByName("TemplateData");
> Templates->Append();  //TADODataSet
> // Write the Modified data bact to a new record.
> // ModBuffer is defined as shown above
> Field1->SetData(ModBuffer,true);
> Templates->UpdateRecord();
>
> I populate other fields using FieldByName->AsString etc.  The 
> new record
> sometimes will show up in the database, but the TemplateData is 
> empty.
>
> Any ideas?
>
> thanks,
> Kev

Hi Kev,

First, I'll show you how we sometimes read fairly small BLOB 
fields.  It's simple.  Then a way of writing them.

// Read
   AnsiString myBlob = qry->Fields->FieldByName( 
"MyBlob" )->AsString;

One note here.  The 'Fields' syntax may be incorrect; I guessed. 
We currently use DB objects that I designed that provide the old 
BDE API because we ported from it.  Use the proper ADO 
FieldByName();


// Writing
   TMemoryStream *MS = new TMemoryStream;
   MS->Write( m_MenuFlags, sizeof(m_MenuFlags) );
   MS->Seek( 0, soFromBeginning );
   qry->Parameters->Items[2]->LoadFromStream( MS, ftBlob );
   delete MS;
   qry->ExecSQL();

Part of the SQL statement is:

   qry->SQL->Add( "UPDATE UserGroup SET Description = :desc, 
Flags = :flgs, "

This writes an unsigned char array (m_MenuFlags) into the BLOB 
field which is parameter 2 (Flags) in the SQL statement.

I hope some of this may be of help to you.

- Arnie

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