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> -> memberOf(valueSetUrl: String) : collection<Boolean>

The memberOf function can be invoked on a collection of Coding or CodeableConcept 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.

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

This function takes a collection of Coding or CodeableConcept 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> -> subsumedBy(code: Coding|CodeableConcept) : 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.