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copied!<p>I debugged the code below with Debug DCUs option activated and the weird thing is that SysUtils.ValidateTimeStamp evaluates a TimeStamp with date = 0 to be invalid and therefore throwing a EConvertError exception (instead of return Null or Unassigned).</p> <p>So the end result is that doing an OldValue request to a null field in a dsInsert state is that its invalid. The variant is <strong>NEVER</strong> returned so it is irrelevant if you test it with (field.OldValue <> Null) or VarIsNull(field.OldValue). The exception gets thrown before.</p> <p>The cds_something has two fields (created at design time):</p> <ul> <li>dt_Something </li> <li>num_something</li> </ul> <p>Code:</p> <pre><code>var b: TClientDataset; begin b := cds_somethin; b.Close; b.CreateDataSet; b.Insert; if b.FieldByName('DT_Sometinhg').OldValue <> Null then ShowMessage('Something wrong!!!') else ShowMessage('Normal'); b.Cancel; </code></pre> <p>Note: I messed up with the original editon of this post. This now is the correct interpretation of what I find.</p> <p>Addition: tested with some other field types (string, BCD, Float and Memo) and OldValue is Unassigned - so the test above will evaluate to false.</p> <p>Appear that ONLY TDateField and TDateTimeField show that behavior. TTimeField and TSQLTimeStamp evaluates normal - but TSQLTimeStampField.OldValue does not equal neither to Null or Unassigned (wtf!!)...</p> <p>The snippet changed a little:</p> <pre><code>var b: TClientDataset; begin b := cds_somethin; b.Close; b.CreateDataSet; b.Insert; /* if (b.FieldByName('DT_Something').OldValue <> Null) and (b.FieldByName('DT_Something').OldValue <> Unassigned) then ShowMessage('Something wrong!!!') else ShowMessage('Normal'); */ if (b.FieldByName('ts_Something').OldValue <> Null) and (b.FieldByName('ts_Something').OldValue <> Unassigned) then ShowMessage('Something wrong!!!') else ShowMessage('Normal'); b.Cancel; </code></pre> <p>Where ts_Something is a TSQLTimeStampField. The fields are created at design time.</p>

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