GetChunkByte Method

Applies To

OraField Object


Reads the data from the LONG or LONG RAW field into byte array and returns the size of data read.


Size_read = orafield.GetChunkByte(ByteArray, offset, numbytes) 


The arguments for the method are:

Arguments Description
ByteArray The first element of the ByteArray to hold the data.
offset The number of bytes in the field to skip before copying data.
numbytes The number of bytes to copy.


When possible, the GetChunkByte method retrieves the specified bytes from the local cache. However, to conserve resources, some of the data might not be stored locally. In these cases, the GetChunkByte method requests the necessary data from the database as required. As part of this process, data from all fields (except the Long or LONG RAW field) in the dynaset are retrieved and compared with the cached values for consistency. If any changes have occurred since the fetch of the original partial data, then the GetChunkByte method stops the operation and an error occurs. In the case of an abort, the returned string is Null.

If a LONG or LONG RAW field is less than 65280 bytes in size, it is quicker to retrieve the data using the Value property than using the GetChunkByte method. You cannot use the GetChunkByte method on a LONG or LONG RAW field for which you have created an alias.


This example demonstrates the use of the GetChunkByte method to retrieve a LONG RAW column of a database and save it as a file. This example expects a valid dynaset named OraDynaset representing a table with a column named longraw. Copy and paste this code into the definition section of a form. Call this procedure with a valid file name.

Sub GetChunkByteExample (FName As String)  
'Declare various variables 
Dim CurSize As Integer, ChunkSize  As Long 
Dim I As Integer, FNum As Integer, CurChunk() As Byte 
'Set the size of each chunk 
ChunkSize = 10240 
'Redim CurChunk Array 
ReDim CurChunk(ChunkSize)  
frmChunk.MousePointer = HOURGLASS  
'Get a free file number 
FNum = FreeFile  
'Open the file 
Open FName For Binary As #FNum  
 I = 0 
'Loop through all of the chunks 
'Oracle does not return the size of columns > 64KB. We should loop until the 'length of our block is less than we asked for.
 CurSize = OraDynaset.Fields("type_longraw").GetChunkByte(CurChunk(0), I * ChunkSize, ChunkSize) 
If CurSize > 0 AND CurSize < ChunkSize Then 
    ReDim CurChunk(CurSize) 
    CurSize = OraDynaset.Fields("type_longraw").GetChunkByte(CurChunk(0), I * ChunkSize, CurSize) 
 End If 
 Put #FNum, , CurChunk   'Write chunk to file. 
 I = I + 1 
Loop Until CurSize <= 0  
'Close the file.  
Close FNum  
frmChunk.MousePointer = DEFAULT  
End Sub

See Also:

"Migration from LONG RAW to LOB or BFILE" for additional information