Share via

Field2.GetChunk Method

  • Article
Access Developer Reference

Returns all or a portion of the contents of a Memo or Long BinaryField2 object in the Fields collection of a Recordset object.

Syntax

expression.GetChunk(Offset, Bytes)

expression   A variable that represents a Field2 object.

Parameters

Name Required/Optional Data Type Description
Offset Required Long The number of bytes to skip before copying begins.
Bytes Required Long The number of bytes you want to return.

Return Value
Variant

Remarks

The bytes returned by GetChunk are assigned to variable. Use GetChunk to return a portion of the total data value at a time. You can use the AppendChunk method to reassemble the pieces.

If offset is 0, GetChunk begins copying from the first byte of the field.

If numbytes is greater than the number of bytes in the field, GetChunk returns the actual number of remaining bytes in the field.

Bb257441.vs_note(en-us,office.12).gif  Note
Use a Memo field for text, and put binary data only in Long Binary fields. Doing otherwise will cause undesirable results.

Example

This example uses the AppendChunk and GetChunk methods to fill an OLE object field with data from another record, 32K at a time. In a real application, one might use a procedure like this to copy an employee record (including the employee's photo) from one table to another. In this example, the record is simply being copied back to same table. Note that all the chunk manipulation takes place within a single AddNew-Update sequence.

Visual Basic for Applications 
  Sub AppendChunkX()

Dim dbsNorthwind As Database
Dim rstEmployees As Recordset
Dim rstEmployees2 As Recordset


Set dbsNorthwind = OpenDatabase("Northwind.mdb")


' Open two recordsets from the Employees table.
Set rstEmployees = _
dbsNorthwind.OpenRecordset("Employees", _
dbOpenDynaset)
Set rstEmployees2 = rstEmployees.Clone


' Add a new record to the first Recordset and copy the
' data from a record in the second Recordset.
With rstEmployees
.AddNew
!FirstName = rstEmployees2!FirstName
!LastName = rstEmployees2!LastName
CopyLargeField rstEmployees2!Photo, !Photo
.Update


  ' Delete new record because this is a demonstration.
  .Bookmark = .LastModified
  .Delete
  .Close



End With


rstEmployees2.Close
dbsNorthwind.Close


End Sub


Function CopyLargeField(fldSource As Field2, _
fldDestination As Field2)


' Set size of chunk in bytes.
Const conChunkSize = 32768


Dim lngOffset As Long
Dim lngTotalSize As Long
Dim strChunk As String


' Copy the photo from one Recordset to the other in 32K
' chunks until the entire field is copied.
lngTotalSize = fldSource.FieldSize
Do While lngOffset < lngTotalSize
strChunk = fldSource.GetChunk(lngOffset, conChunkSize)
fldDestination.AppendChunk strChunk
lngOffset = lngOffset + conChunkSize
Loop


End Function