[HAPI-devel] Can't find ZRT as a direct child error for custom Hl7 segments

[Shreeja J <mai...@gm...>]

Hello Team,

I am encountering an issue while parsing HL7 messages with a custom segment
(ZRT) .I am using:

   -

   *Java 21*
   -

   *Spring Boot 3.3.3*
   -

   *GenericParser* from HAPI HL7 v2
   -

   Supporting HL7 versions *v23 through v28*

When I try to access the custom segment using Terser, I get the following
exception:

```

ca.uhn.hl7v2.HL7Exception: Can't find ZRT as a direct child
    at ca.uhn.hl7v2.util.SegmentFinder.getStructure(SegmentFinder.java:141)
    at ca.uhn.hl7v2.util.SegmentFinder.getSegment(SegmentFinder.java:108)
    at ca.uhn.hl7v2.util.Terser.getSegment(Terser.java:358)
    at ca.uhn.hl7v2.util.Terser.get(Terser.java:324)
    at
org.techbd.ingest.service.ZrtSegmentParserTest.assertZrtFields(ZrtSegmentParserTest.java:63)
    at
org.techbd.ingest.service.ZrtSegmentParserTest.testCustomSegmentAfterPID(ZrtSegmentParserTest.java:49)
```

  I am including the full *JUnit test* file for reference.

```
package org.service;

import ca.uhn.hl7v2.HL7Exception;
import ca.uhn.hl7v2.model.Message;
import ca.uhn.hl7v2.parser.GenericParser;
import ca.uhn.hl7v2.util.Terser;
import ca.uhn.hl7v2.validation.impl.NoValidation;
import org.junit.jupiter.api.DisplayName;
import org.junit.jupiter.api.Test;

import static org.assertj.core.api.Assertions.assertThat;

public class ZrtSegmentParserTest {

    private final GenericParser parser;

    public ZrtSegmentParserTest() {
        parser = new GenericParser();
        parser.setValidationContext(new NoValidation()); // Disable HL7
validation
    }

    // ---------------------------
    // Sample HL7 Messages
    // ---------------------------

    private static final String HL7_PUSH =
            "MSH|^~\\&||DUMMYHOSP|||||ORU^R01|||2.5\r" +

"PID||123456^^^DUMMY:FACID^MRN|123456^^^DUMMY:FACID^MRN||Doe^John^A||19800101|M\r"
+

"ZRT||ORU|R01|PUSH|||||123456^dummy:ABC~654321^dummy:XYZ|abcdef123456|userId^Test^User|add";

    private static final String HL7_PBRD_ZRT_AFTER_MSH =
            "MSH|^~\\&||DUMMYHOSP|||||ORU^R01|||2.5\r" +

"ZRT||ORU|R01|PBRD|||A1^DOE^JANE^ABC^ATT~B2^DOE^JANE^XYZ^CON|dummy:FAC|987654^dummy:ABC~456789^dummy:XYZ|abcdef987654||\r"
+

"PID||123456^^^DUMMY:FACID^MRN|123456^^^DUMMY:FACID^MRN||Doe^John^A||19800101|M";

    // ---------------------------
    // Tests
    // ---------------------------

    @Test
    @DisplayName("Test ZRT segment after MSH")
    void testCustomSegmentAfterMSH() throws HL7Exception {
        assertZrtFields(HL7_PBRD_ZRT_AFTER_MSH, "PBRD", "dummy:FAC", "ORU");
    }

    @Test
    @DisplayName("Test ZRT segment after PID")
    void testCustomSegmentAfterPID() throws HL7Exception {
        assertZrtFields(HL7_PUSH, "PUSH", "dummy:ABC", "ORU");
    }

    // ---------------------------
    // Helper Method
    // ---------------------------

    private void assertZrtFields(String hl7Message, String
expectedDeliveryType,
                                 String expectedFacility, String
expectedMessageCode) throws HL7Exception {

        Message message = parser.parse(hl7Message);

        Terser terser = new Terser(message);

        String messageCode = terser.get("/ZRT-2");
        String triggerEvent = terser.get("/ZRT-3");
        String deliveryType = terser.get("/ZRT-4");
        String facility = terser.get("/ZRT-8");

        assertThat(messageCode).isEqualTo(expectedMessageCode);
        assertThat(triggerEvent).isNotEmpty();
        assertThat(deliveryType).isEqualTo(expectedDeliveryType);
        assertThat(facility).isEqualTo(expectedFacility);

        System.out.printf("ZRT parsed: %s | %s | %s | %s%n",
                messageCode, triggerEvent, deliveryType, facility);
    }
}
```




*Dependencies Used:```*<dependency>
    <groupId>ca.uhn.hapi</groupId>
    <artifactId>hapi-base</artifactId>
    <version>${hapi.version}</version>
</dependency>
<dependency>
    <groupId>ca.uhn.hapi</groupId>
    <artifactId>hapi-structures-v23</artifactId>
    <version>${hapi.version}</version>
</dependency>
<dependency>
    <groupId>ca.uhn.hapi</groupId>
    <artifactId>hapi-structures-v24</artifactId>
    <version>${hapi.version}</version>
</dependency>
<dependency>
    <groupId>ca.uhn.hapi</groupId>
    <artifactId>hapi-structures-v25</artifactId>
    <version>${hapi.version}</version>
</dependency>
<dependency>
    <groupId>ca.uhn.hapi</groupId>
    <artifactId>hapi-structures-v26</artifactId>
    <version>${hapi.version}</version>
</dependency>
<dependency>
    <groupId>ca.uhn.hapi</groupId>
    <artifactId>hapi-structures-v27</artifactId>
    <version>${hapi.version}</version>
</dependency>
<dependency>
    <groupId>ca.uhn.hapi</groupId>
    <artifactId>hapi-structures-v28</artifactId>
    <version>${hapi.version}</version>
</dependency>
```

*Question:*
  How can I correctly parse a custom segment like ZRT using Terser when it
may appear *anywhere in the message* (not necessarily after MSH)? Is there
a recommended way to register custom segments so they can be reliably
accessed, regardless of their position?

Any thoughts on this?

Thank you for your guidance!


Shreeja