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FHIR-specific functions

The following functions are defined in the FHIR specification as additional FHIRPath functions for use with FHIR data.

The notation used to describe the type signature of each function is as follows:

[input type] -> [function name]([argument name]: [argument type], ...): [return type]

extension​

collection<Element> -> extension(url: String) : collection<Extension>

Filters the input collection to only those elements that have an extension with the specified URL. This is a shortcut for .extension.where(url = string).

Example:

Patient.extension('http://hl7.org/fhir/StructureDefinition/patient-birthPlace')

resolve​

collection<Reference> -> resolve() : collection<Resource>

For each Reference in the input collection, returns type information about the resource that the reference points to.

How it works​

The resolve() function extracts resource type information from Reference elements using the following priority:

  1. Uses the Reference.type field if present (highest priority)
  2. Parses the type from the Reference.reference string (e.g., Patient/123 → Patient type)
  3. Returns an empty collection when the type cannot be determined

This supports relative references (Patient/123), absolute references (http://example.org/fhir/Patient/123), and canonical URLs.

Usage with type operators​

The primary use case for resolve() is type checking and filtering with the is and ofType() operators:

Encounter.subject.resolve() is Patient
Patient.generalPractitioner.resolve().ofType(Practitioner)
Patient.generalPractitioner.where(resolve() is Organization)

Limitations​

The resolve() function in Pathling extracts type information only and does not support field traversal. Attempting to access fields on a resolved reference (e.g., resolve().name) will result in an error.

For accessing data from referenced resources, use the reverseResolve() function instead. See Extension functions for details.

memberOf​

collection<Coding|CodeableConcept|Quantity> -> memberOf(valueSetUrl: String) : collection<Boolean>

The memberOf function can be invoked on a collection of Coding, CodeableConcept or Quantity values, returning a collection of Boolean values based on whether each concept is a member of the ValueSet with the specified url.

For a CodeableConcept, the function will return true if any of the codings are members of the value set.

For a Quantity, the concept is the coded unit — see Quantity as a concept.

note

The memberOf function is a terminology function, which means that it requires a configured terminology service. See Terminology functions for details.

subsumes​

collection<Coding|CodeableConcept|Quantity> -> subsumes(code: Coding|CodeableConcept|Quantity) : collection<Boolean>

This function takes a collection of Coding, CodeableConcept or Quantity elements as input, and another collection as the argument. The result is a collection with a Boolean value for each source concept, each value being true if the concept subsumes any of the concepts within the argument collection, and false otherwise.

Example:

Patient.reverseResolve(Condition.subject).code.subsumes(http://snomed.info/sct|770581008)
note

The subsumes function is a terminology function, which means that it requires a configured terminology service. See Terminology functions for details.

subsumedBy​

collection<Coding|CodeableConcept|Quantity> -> subsumedBy(code: Coding|CodeableConcept|Quantity) : collection<Boolean>

The subsumedBy function is the inverse of the subsumes function, examining whether each input concept is subsumed by any of the argument concepts.

Example:

Patient.reverseResolve(Condition.subject).code.subsumedBy(http://snomed.info/sct|73211009)
note

The subsumedBy function is a terminology function, which means that it requires a configured terminology service. See Terminology functions for details.

Quantity as a concept​

The terminology functions that operate upon concepts — memberOf, subsumes, subsumedBy and translate — can also be invoked on a Quantity. The concept is the coded unit of the quantity, taken from its system and code, with the unit as the display. The value of the quantity plays no part.

This allows units of measure to be checked against a value set, or mapped to another set of unit codes:

Observation.value.ofType(Quantity).translate('https://csiro.au/fhir/ConceptMap/units')

The original unit code is used, rather than the canonical form that Pathling derives for the purposes of comparison, as a ConceptMap or ValueSet is authored against the codes that appear within the data.

A quantity that carries only a free-text unit, without a system and code, does not identify a concept. Such a quantity yields false from memberOf, subsumes and subsumedBy, and an empty result from translate — the same behaviour as a Coding without a system and code.