Tag Value Delta Calculation

Ignition
10

Candidate fixed module.

There’s a bit of a visual issue remaining that I don’t plan to fix. The output of the recorder() function (and the view() function, too) is a TransientDataset, not a normal Dataset. This type of dataset serializes to zero rows. It is intended to prevent bloated project resources when datasets are part of a component. This means that recorder() output will always show zero rows in the designer, even though they really are there in the gateway. Here’s an export of a set of tags testing and demonstrating this behavior. The Recording tag shows in the tag browser with zero rows, even though it ends up with twenty rows.

<Tags>
   <Tag name="SimRecord" path="" type="Folder"/>
   <Tag name="Delta" path="SimRecord" type="DB">
      <Property name="Value">0.0</Property>
      <Property name="DataType">4</Property>
      <Property name="ExpressionType">1</Property>
      <Property name="Expression">{[.]Source}-try({[.]Recording}[0, &apos;Source&apos;], {[.]Source})</Property>
   </Tag>
   <Tag name="Recording" path="SimRecord" type="DB">
      <Property name="Value">
         <Dataset>
            <columns>
               <col name="t_stamp" datatype="DateTime"/>
               <col name="Source" datatype="Float4"/>
            </columns>
            <rows>
            </rows>
         </Dataset>
      </Property>
      <Property name="DataType">9</Property>
      <Property name="ExpressionType">1</Property>
      <Property name="Expression">recorder(1000, 20,  &quot;Source&quot;, {[.]Source})</Property>
   </Tag>
   <Tag name="RecordingLen" path="SimRecord" type="DB">
      <Property name="Value">20</Property>
      <Property name="DataType">2</Property>
      <Property name="ExpressionType">1</Property>
      <Property name="Expression">len({[.]Recording})</Property>
   </Tag>
   <Tag name="Source" path="SimRecord" type="DB">
      <Property name="Value">6.0</Property>
      <Property name="DataType">4</Property>
   </Tag>
</Tags>

For some reason, the rows do display in earlier Ignition versions, in spite of the TransientDataset return.

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