ID is always added to output even input message doesn't have id

[kthaya]

Describe the bug When a message string converted from JSON to XML or XML to JSON, ID is always added to output even input message doesn't have id. I don't see anywhere in FHIR specification to mention that ID is mandatory.

To Reproduce

1. Create a JSON/XML message string without ID string
2. Parse the message with hapi library
3. Output contains ID tag

Expected behavior Output should not contain ID tag

Environment (please complete the following information):

• HAPI FHIR Version -2.5
• all os Additional context It looks like ID is always extracted from fullURL based on following code: https://github.com/jamesagnew/hapi-fhir/blob/a952663dc323c727436c4218f70bd13f8421604f/hapi-fhir-base/src/main/java/ca/uhn/fhir/parser/BaseParser.java#L697

[jamesagnew]

I'm not sure I follow- Could you please provide a code snippet which demonstrates this issue?

[kthaya]

import odl.ca.uhn.fhir_2_5.context.FhirContext;
import odl.org.hl7.fhir_2_5.dstu3.model.Bundle;
import odl.ca.uhn.fhir_2_5.parser.IParser;

public class HapiSetIdTest {

    public static void main(String[] args) throws Exception {
        FhirContext ctxDstu2 = FhirContext.forDstu3();

        String input = "<Bundle xmlns=\"http://hl7.org/fhir\"><id value=\"bundle-example\" /><entry><fullUrl value=\"https://example.com/base/MedicationRequest/3123\"/>"
                + "<resource><MedicationRequest></MedicationRequest></resource></entry></Bundle>";
        IParser parser = ctxDstu2.newXmlParser();

        Bundle output = (Bundle) parser.parseResource(input);

        System.out.println(parser.encodeResourceToString(output));

    }

}

Question is why output has id tag \\ while input doesn't have?

Output

<Bundle xmlns="http://hl7.org/fhir"><id value="bundle-example"></id><entry><fullUrl value="https://example.com/base/MedicationRequest/3123"></fullUrl><resource><MedicationRequest xmlns="http://hl7.org/fhir"><id value="3123"></id></MedicationRequest></resource></entry></Bundle>

Input

<Bundle xmlns="http://hl7.org/fhir"><id value="bundle-example"/><entry><fullUrl value="https://example.com/base/MedicationRequest/3123"/><resource><MedicationRequest></MedicationRequest></resource></entry></Bundle>

[jamesagnew]

That 3123 comes from the fullUrl tag. It is by design, since that is the purpose of that field.

[kthaya]

Thanks, when I look at FHIR spec identity is still optional (0..1) - https://www.hl7.org/fhir/medicationrequest-definitions.html#MedicationRequest.identifier

[jamesagnew]

FYI: MedicationRequest.identifier is different from MedicationRequest.id

The id field is optional too, but certainly in this specific use case, if you're parsing a Bundle that provides an ID via the fullUrl field, I believe it's the right behaviour to respect it. Can you not just clear it if manually after parsing you need different behaviour?