Support direct-reference codes for plural terminology targets

[brynrhodes]

The retrieve operation supports both value sets and direct-reference codes as the terminology target for a retrieve. However, if the path for that terminology target results in a multi-cardinality element, value sets work, but direct-reference codes do not, resulting in an error that the terminology target cannot be resolved:

library EncounterTest

using QICore version '4.1.1'

include FHIRHelpers version '4.2.000'

codesystem "Concept Codes": 'http://example.org/fhir/CodeSystem/concept-codes'

valueset "Inpatient Encounters": 'http://hl7.org/fhir/ValueSet/inpatient-encounters'

code "Inpatient": 'inpatient' from "Concept Codes"

context Patient

define "Encounters By ValueSet":
  ["Encounter": "Inpatient Encounters"]

define "Encounters By Code":
  ["Encounter": "Inpatient"]

The issue is that the retrieve would require the following:

define "Encounters By Code":
  ["Encounter"] E
    where exists ((E.type) T where T ~ "Inpatient")

Alternatively, an overload of the equivalent operation:

~(List<Code>, Code)

[brynrhodes]

Note this is related to CQLIT-368. The workaround is to use a ValueSet (i.e. create a value set with the direct-reference code required and use that value set).