This mechanism is used when the size of the buffer available is smaller than
the total amount of data to be read. The total amount of data to be read is set
by using the PollingAmount (OraLOB/BFILE) property. The Offset (OraLOB/BFILE) property is used only once to set the offset for the first piece read
operation. After the first time, it is automatically increased by the size of the
previous piece.
The Status (OraLOB/BFILE) property must be checked for success of each piece read operation. If Status
property returns ORALOB_NEED_DATA, the Read method must be called again. This
must continue until the amount specified by PollingAmount property has been
read. At the end of multiple piece operation, the Status property returns
ORALOB_NO_DATA.
The following example reads 102k of data in 10k chunks from the part_image
column at offset of 1000 to the local file 'image.dat'.
Dim buffer as Variant
Dim buf() As Byte
Set OO4OSession = CreateObject("OracleInProcServer.XOraSession")
Set InvDb = OO4OSession.OpenDatabase("INVDB", "scott/tiger", 0)
Set Part = InvDb.CreateDynaset("select * from part", 0&)
Set PartImage = Part.Fields("part_image").Value
FNum = FreeFile
Open "image.dat" For Binary As #FNum
PartImage.offset = 1000
PartImage.PollingAmount = 102000
amount_read = PartImage.Read(buffer, chunksize)
buf = buffer
Put #FNum, , buf
While PartImage.Status = ORALOB_NEED_DATA
amount_read = PartImage.Read(buffer, chunksize)
buf = buffer
Put #FNum, , buf
Wend
Close FNum
The previous lines of code read the part_image LOB data and writes it to image.dat file . At the end of the multiple piece operation, the Status property
returns ORALOB_NO_DATA.
