save BLOB to file from MySQL using c#

[Markusek Peter]

Hi,
I'm using MySQLDriverCS. I've got no problem to store BLOB into database,
but I can't get it back(save to file).
Problem is with DataTable(retur ns string:( )
My code:
--
DataTable dt = new MySQLSelectComm and(...; //select that row and column
where is BLOB
string dest = Server.MapPath( "image.jpg" );
FileStream binFile = new
FileStream(dest ,FileMode.OpenO rCreate,FileAcc ess.Write);
--
Now I want to use - binFile.Write(b uf,0,buf.Length );. But problem is that
dt.Rows[0]["ColumnBLOB "] is System.String type, and I need byte[](for
binFile.Write)
When I use this function :
--
public byte[] Serialize(objec t o)
{
MemoryStream s = new MemoryStream();
BinaryFormatter b = new BinaryFormatter ();
b.Serialize(s, o);
if (s.Length > int.MaxValue)
throw new ArgumentExcepti on("Serialized object is larger than can fit into
byte array");
byte[] buffer = new Byte[s.Length];
s.Seek(0, SeekOrigin.Begi n);
s.Read(buffer, 0, (int)s.Length);
s.Close();
return buffer;
}
--
BLOB is saved into the file with the right size, but most of the characters
are '?'(because
dt.Rows[0]["ColumnBLOB "] is string?)

=============== ======
I'm sorry for bad english.
Sample code will be appreciated:)
Thanks.

[Markusek Peter]

I did it with ByteFX drivers, because MySQLDriverCS has not defined
methods(like MySQLDataReader .GetBytes(...) )

Here is sample code-
--
string connectionStrin g =

"Server=localho st;" +

"Database=iso_d okumentacia;" +

"User ID=;" +

"Password=; ";

MySqlConnection cn = new MySqlConnection (connectionStri ng);
FileStream fs; // Writes the BLOB to a file (*.jpg).

BinaryWriter bw; // Streams the BLOB to the FileStream object.

int bufferSize = 100; // Size of the BLOB buffer.

byte[] outbyte = new byte[bufferSize]; // The BLOB byte[] buffer to be
filled by GetBytes.

long retval; // The bytes returned from GetBytes.

long startIndex = 0; // The starting position in the BLOB output.
cn.Open();

MySqlCommand logoCMD = new MySqlCommand("S ELECT KapitolaBLOB FROM kapitola
WHERE ID_KAPITOLA=15" ,cn);
MySqlDataReader myReader =
logoCMD.Execute Reader(CommandB ehavior.Sequent ialAccess);

while (myReader.Read( ))

{

// Get the publisher id, which must occur before getting the logo.
// Create a file to hold the output.

string dest = Server.MapPath( "s.jpg");

fs = new FileStream(dest , FileMode.OpenOr Create, FileAccess.Writ e);

bw = new BinaryWriter(fs );

// Reset the starting byte for the new BLOB.

startIndex = 0;

// Read the bytes into outbyte[] and retain the number of bytes returned.

//myReader.GetByt es(0, startIndex, outbyte, 0, bufferSize);

retval =(long) myReader.GetByt es(0, startIndex, outbyte, 0, bufferSize);

// Continue reading and writing while there are bytes beyond the size of the
buffer.

while (retval == bufferSize)

{

bw.Write(outbyt e);

bw.Flush();

// Reposition the start index to the end of the last buffer and fill the
buffer.

startIndex += bufferSize;

retval = myReader.GetByt es(0, startIndex, outbyte, 0, bufferSize);

}

// Write the remaining buffer.

bw.Write(outbyt e, 0, (int)retval - 1);

bw.Flush();

// Close the output file.

bw.Close();

fs.Close();

}

myReader.Close( );

cn.Close();

}

--