Perspective Custom Props losing Type

Ignition
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1

Hoping for a nudge, I want to return tag data for a specific path. The example below works in the Designer. Tag paths are BasicTagPath and values are BasicQualifiedValue. But, when I bind the results (using script transform) in a custom prop within Perspective everything seems to lose their type. For example the value is not a QV, it is the actual value or None/null if bad quality.

results = [tag for tag in system.tag.browse(tagPath, {"valueSource":"opc", "recursive":True})]

What am I missing?

2

Anything assigned to a Perspective property is coerced into a type that is JSON compatible, or with a thin wrapper, because that's how they have to travel to the browser. And has been this way from day one.

This is one of the motivations for sessionVarMap(), pageVarMap(), and viewVarMap(), as implemented in my Integration Toolkit module. You can bring values into Perspective through those maps, and the Perspective side will be coerced, but a script can retrieve the values in their original jython/java glory.

(Though, having the equivalent of page custom properties was also a consideration. Two birds with one stone, and all that.)

3

Hey Phil, just to make sure I'm understanding, BasicTagPath and/or BasicQualifiedValue are not JSON compatible types?

4

Nope. You get:

  • Strings
  • Numbers
  • Arrays
  • Mappings { But the keys must be proper javascript identifiers }
  • Datasets { not native to JSON, but implemented as a light wrapper with the above }
1 Like
5

Thank you. Good info to know.