In A TPacketDataSet->Data usModified record, How can I determine which fields carry NULL value because they were deliberately changed to NULL?

Question

I copy the TClientDataSet->Delta to TPacketDataSet->Data. Then I am using TPacketDataSet->Data to write cached updates to Faircom Server ISAM database record. When using the Modified Record pair, The second copy of the record marked "usModified" holds every field, modified or not, with the unmodified fields carrying NULL as the NewValue. Question: How can I determine which fields carry NULL value because they were deliberately changed to NULL, and which fields are NULL because they weren't changed? Simply writing NewValue to the persistence layer would result in clearing all field values which were not changed.

What about checking the field's [OldValue](http://docwiki.embarcadero.com/Libraries/en/Data.DB.TField.OldValue)? — Victoria, Feb 01 '18 at 19:58
It really doesn't help. If NewValue is NULL if not changed, and NULL if changed to NULL, comparing it to OldValue doesn't clarify the intention. — Alan Taylor, Feb 02 '18 at 02:36

score 0 · Accepted Answer · answered Feb 02 '18 at 05:59

0

use InitAltRecBuffers and see if NewValue is Unassigned (not changed) or Null (cleaned)

answered Feb 02 '18 at 05:59

Vladimir Ulchenko

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Are you able to provide an example? – Alan Taylor Feb 02 '18 at 20:47
Thank you vavan. Testing NewValue for VarIsEmpty (Unassigned) was the solution. – Alan Taylor Feb 04 '18 at 21:40

In A TPacketDataSet->Data usModified record, How can I determine which fields carry NULL value because they were deliberately changed to NULL?

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