Field.GetChunk Method (DAO)
Last modified: March 09, 2015
Applies to: Access 2013 | Office 2013
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.
Use a Memo field for text, and put binary data only in Long Binary fields. Doing otherwise will cause undesirable results.
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.
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 Field, _ fldDestination As Field) ' 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