Navigating FHIR Resources

The FHIR resources returned from FHIR requests are instances of models defined in the fhir_models gem. These models provide methods to access the fields in a FHIR resource.

resource.id # returns a String containing the resource id

# Assuming this resource is a Patient:
resource.name # returns an Array of FHIR::HumanName
resource.name.first.family # returns a String containing the family name in the
                           # Patient's first name. This is not nil-safe! An
                           # error will be raised if resource.name is nil.

FHIR resources can be deeply nested, and navigating through deeply nested models while also managing nil-safety can be cumbersome, so several methods are provided to make it easier and safer to extract information from FHIR resources.

resolve_path returns an Array containing all the values found at a given path, or an empty Array if no values are found.

patient_without_names = FHIR::Patient.new(id: 'no-names')
patient_with_a_name = FHIR::Patient.new(id: 'one-name', name: [{ family: 'ABC' }])
patient_with_names = FHIR::Patient.new(id: 'one-name', name: [{ family: 'ONE' }, { family: 'TWO' }])
resolve_path(patient_without_names, 'name')        # []
resolve_path(patient_without_names, 'name.family') # []
resolve_path(patient_with_a_name, 'name')          # [FHIR::HumanName(family: 'ABC')]
resolve_path(patient_with_a_name, 'name.family')   # ['ABC']
resolve_path(patient_with_names, 'name')           # [FHIR::HumanName(family: 'ONE'), FHIR::HumanName(family: 'TWO')]
resolve_path(patient_with_names, 'name.family')    # ['ONE', 'TWO']

find_a_value_at only returns a single value from a given path. An optional block can be provided to return the first value at a particular path for which the block returns a truthy value. This method is particularly useful for finding values from a given resource to use as values for search parameters.

patient_without_names = FHIR::Patient.new(id: 'no-names')
patient_with_a_name = FHIR::Patient.new(id: 'one-name', name: [{ family: 'ABC' }])
patient_with_names = FHIR::Patient.new(id: 'one-name', name: [{ family: 'ONE' }, { family: 'TWO' }])
find_a_value_at(patient_without_names, 'name.family') # nil
find_a_value_at(patient_with_a_name, 'name.family')   # 'ABC'
find_a_value_at(patient_with_names, 'name.family')    # 'ONE'

find_a_value_at(patient_without_names, 'name.family') { |family| family == 'ABC' } # nil
find_a_value_at(patient_with_a_name, 'name.family') { |family| family == 'ABC' }   # 'ABC'
find_a_value_at(patient_with_names, 'name.family') { |family| family == 'ABC' }    # nil

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