FHIR Chat · FHIRPathEngine ignores annotated Extensions · hapi

Stream: hapi

Topic: FHIRPathEngine ignores annotated Extensions

Sergej Reiser (Sep 24 2020 at 14:46):

The FHIRPathEngine is not seeing Extensions, that have been added by using the Field-Annotations @Child / @Extension.

Lets say i have the following class for MyPatient (just like in the HAPI documentation):

@ResourceDef(name="Patient", profile="http://example.com/StructureDefinition/mypatient")
public class MyPatient extends Patient {
    private static final long serialVersionUID = 1L;

    @Child(name="petName")
    @Extension(url="http://example.com/dontuse#petname", definedLocally=false, isModifier=false)
    @Description(shortDefinition="The name of the patient's favourite pet")
    private StringType myPetName;

    @Override
    public boolean isEmpty() {
        return super.isEmpty() && ElementUtil.isEmpty(myPetName);
    }

    public StringType getPetName() {
        if (myPetName == null) {
            myPetName = new StringType();
        }
        return myPetName;
    }

    public void setPetName(StringType thePetName) {
        myPetName = thePetName;
    }
}

Now i would like to read the Extension with a FHIR-Path expression.

@Test
void readByFhirPath() throws Exception {
    IFhirPath fhirPath = FhirContext.forR4().newFhirPath();

    MyPatient myPatient = new MyPatient();
    myPatient.setPetName(new StringType("Adam"));
    // notice: myPatient.getExtension() is empty

    List<Extension> result = fhirPath.evaluate(myPatient, "Patient.extension('http://example.com/dontuse#petname')", Extension.class);
    assert result.size() == 1; // fails, because the list is empty
}

This fails! But when i add the Extension the "old-fsahion" way everything is fine!

@Test
void readByFhirPath() throws Exception {
    IFhirPath fhirPath = FhirContext.forR4().newFhirPath();

    MyPatient myPatient = new MyPatient();
//    myPatient.setPetName(new StringType("Adam"));
    myPatient.addExtension(new Extension("http://example.com/dontuse#petname", new StringType("Adam")));

    List<Extension> result = fhirPath.evaluate(myPatient, "Patient.extension('http://example.com/dontuse#petname')", Extension.class);
    assert result.size() == 1; // succeeds
}

Im not sure if this is an Issue with the FHIRPathEngine itself, or rather with the fact, that annotated Extensions are not accessable through resource.getExtension(). Is there some kind of a workaround to this?

Sergej Reiser (Oct 21 2020 at 08:51):

PUSH
Could someone please look into this? The circumstance, that FHIR-Path is not working for annotated Extensions has further implications for indexing of SearchParams.

If i create a custom SearchParameter for petName it will not work, because HAPI also uses FHIR-Path for indexing. So this is what happens:
Before indexing or persisting, HAPI will parse the resource into it's corresponding class. If i added theMyPatient class to the FhirContext by fhirContext.setDefaultTypeForProfile("http://example.com/StructureDefinition/mypatient", MyPatient.class), HAPI will parse the resource into MyPatient and further pass this object for indexing. Since MyPatient uses the @Extension annotation FHIR-Path will fail to evaluate the expression i use for my SearchParameter (Patient.extension('http://example.com/dontuse#petname')). So petName will never be indexed as long as HAPI uses the MyPatientclass for processing.

The only workaround i found is to temporarily remove the MyPatient class from the FHIR-Context fhirContext.setDefaultTypeForProfile("http://example.com/StructureDefinition/mypatient", null). Than HAPI will parse incoming resources into the default Patient class which has no @Extension annotations.

Last updated: Apr 12 2022 at 19:14 UTC