Attributes on union output not accessible, not yielding expected calculation results

[nmorasb]

It seems that the output of a union inside a library is not allowing access to properties of the union types.
We have a define in a library performing a union:

Usage showing attributes are not hit:

Usage in the denominator exclusion:

It seems like the attributes performed and authoredOn of ComfortMeasure may not be accessible and are both returning null.

The measure bundle and patient bundle are attached for reference.
union-output-issue.zip

@JSRankins

[srankins]

For whoever looks at this, just to clarify, I think the issue occurs whenever the union results in a choice type. Note: a similar issue occurred with cql-engine. Refer to CQLIT-329.

[mgramigna]

@nmorasb @srankins

Thanks! I was able to replicate the issue in fqm-execution. We will try working with a simpler test case I created that also demonstrates this issue:

library UnionTest version '1.0.000'
 
using QICore version '4.1.1'

include FHIRHelpers version '4.1.000' called FHIRHelpers
include QICoreCommon version '1.2.000' called QICoreCommon

parameter "Measurement Period" Interval<DateTime>

context Patient

define "Union Issue":
  ([Procedure] union [ServiceRequest]) ComfortMeasure
    return {
      cmPerformed: ComfortMeasure.performed,
      cmAuthoredOn: ComfortMeasure.authoredOn,
      coalesced: Coalesce(start of QICoreCommon."ToInterval"(ComfortMeasure.performed), ComfortMeasure.authoredOn)
    }

Currently, all of the values in this returned object are null, which shouldn't be the case given the patient bundle that you've provided.

I logged a ticket in our backlog. Will let you know what the path forward is (be it here, cql-execution, or translator).

[mgramigna]

Also likely relevant is these errors that are logger during execution (which I think actually come from cql-exec-fhir). This usually indicates an issue with the ELM

[mgramigna]

@nmorasb @srankins last question. Which version of the translator are you using? Just to make sure we have the latest if we try to replicate this with other CQL.

[nmorasb]

Interesting! We're on cqframework version 2.4.0.

[mgramigna]

@srankins @nmorasb We investigated this a bit. Before proceeding, I think we need more clarification from @brynrhodes on how the translator is expected to handle accessing properties on a choice type when in the context of a union like this. Take the following CQL:

define "Single":
  [Procedure] P
    return {
      perf: P.performed
    }

define "Union of Same Type":
 ([Procedure] union [Procedure]) P
    return {
      perf: P.performed
    }

define "Union of Different Types":
  ([Procedure] union [ServiceRequest]) ComfortMeasure
    return {
      cmPerformed: ComfortMeasure.performed,
      cmAuthoredOn: ComfortMeasure.authoredOn,
    }

The "Union of Different Types" expression is the only one whose ELM raises concerns (which aligns with what Stan said in his comment above). Here are the corresponding ELM snippets of the elements in the above Tuples:

// from "Single" expression above
{
  "name": "perf",
  "value": {
    "name": "ToValue",
    "libraryName": "FHIRHelpers",
    "type": "FunctionRef",
    "operand": [
      {
        "path": "performed",
        "scope": "P",
        "type": "Property"
      }
    ]
  }
}

// from "Union of Same Type" expression above
{
  "name": "perf",
  "value": {
    "name": "ToValue",
    "libraryName": "FHIRHelpers",
    "type": "FunctionRef",
    "operand": [
      {
        "path": "performed",
        "scope": "P",
        "type": "Property"
      }
    ]
  }
}

// from "Union of Different Types" expression above
{
  "name": "cmPerformed",
  "value": {
    "path": "FHIRHelpers.ToValue(%value)",
    "scope": "ComfortMeasure",
    "type": "Property"
  }
},
{
  "name": "cmAuthoredOn",
  "value": {
    "path": "%value.value",
    "scope": "ComfortMeasure",
    "type": "Property"
  }
},
{
  "name": "coalesced",
  "value": {
    "type": "Coalesce",
    "operand": [
      {
        "type": "Start",
        "operand": {
          "name": "ToInterval",
          "libraryName": "QICoreCommon",
          "type": "FunctionRef",
          "operand": [
            {
              "path": "FHIRHelpers.ToValue(%value)",
              "scope": "ComfortMeasure",
              "type": "Property"
            }
          ]
        }
      },
      {
        "path": "%value.value",
        "scope": "ComfortMeasure",
        "type": "Property"
      }
    ]
  }
}

Note the appearances of FHIRHelpers.ToValue(%value) and %value.value. These are present in the QI Core ModelInfo, but appear to be unwrapped in the other cases but not this one (i.e. FHIRHelpers.ToValue(%value) is translated to an ELM function ref by the translator instead of being used as the literal path).

My suspicion is that the translator needs to be unwrapping these strings with % during translation, and that is not being done for some reason when accessing the properties on the result of a union of different types. As written, the above ELM is telling the engine to look for a literal property named "FHIRHelpers.ToValue(%value)" on a FHIR Procedure resource, which obviously doesn't exist. Hopefully Bryn can clarify

[brynrhodes]

Yes, that is definitely a bug, the translator is not expanding the mappings in this case. Can you submit this as an issue to the translator?

[mgramigna]

Closing in favor of cqframework/clinical_quality_language#1126