Parsing ORU_01 doesn't let me access all segements

[jerchap]

Just started using NHAPI and trying to understand how it parses messages, and how you access segments.

I have an HL7 message like this:

MSH|^~\&|IHAOE^2.1|IHRIH|ITS||202305101401||ORU^R01|J2317804|D|2.3|||AL|NE|
EVN|001|202305101358|
PID|1|A0-B20210413102902338|KA00001155|9874146262|Creek^Sandi^^^^^L||20080204|F|||2000 Doggy Way^^Cranbrook^BC^V1C 0A9||250-919-0777|||||KA0003152/23|9874146262||||||||||||||||F| PV1|1|I|KAMRIHAED9^RIHAED901^01|EL|||TST^Test^Test^E^^|||MED||||HO|||TST^Test^Test^E^^|IN||BC|||||||||||||||||||IHRIH||ADM|||202212221429||||||||TST^Test^Test^E^^|
ORC|1|
OBR|1||13553IHRIH|WEB.PT^Operative Report^^11504-8^Operative Note^pCLOCD|||202305101355|202305101355|||||IHRIH|||BBM1^Bil^Bob^Moore^^Dr||||WEB.PT|W2.OR-P|202305101358||OE|S|||TST^Test^Test^E^^~^Test^Test^E^^||||BBM1^Bil^Bob^Moore^^Dr|||BBM1^Bil^Bob^Moore^^Dr|
OBX|1|TX||| Test |
OBX|2|TX||| Test2 |
ZDR||TST^Test^Test^E^^^TEST^^^^^^^^ATP^~BBM1^Bil^Bob^Moore^^Dr^MD RCPSC^^^^^^^^ATP^||TST^Test^Test^E^^^TEST^^^^^^^^FAP^|

I parse it like this:

var message = parser.Parse(hl7, new ParserOptions()
            {
                UnexpectedSegmentBehaviour = UnexpectedSegmentBehaviour.AddInline
            });

I can access the MSH and EVN segments by using the GetStructure method:
message.GetStructure("MSH")

But I can't access the OBX, ORC, OBR, PID or custom ZDR segment using GetStructure.

If I convert the message to xml like this:

var xmlParser = new DefaultXMLParser();
 var xml = xmlParser.Encode(message);

I get the following structure:

<?xml version="1.0" encoding="utf-8"?>
<ORU_R01 xmlns="urn:hl7-org:v2xml">
  <MSH>
    ...
  </MSH>
  <EVN>
    ...
  </EVN>
  <ORU_R01.RESPONSE>
    <ORU_R01.PATIENT>
      <PID>
        ...
      </PID>
    </ORU_R01.PATIENT>
    <ORU_R01.ORDER_OBSERVATION>
      <ORC>
        ...
      </ORC>
      <OBR>
        ...
      </OBR>
      <ORU_R01.OBSERVATION>
        <OBX>
          ...
        </OBX>
      </ORU_R01.OBSERVATION>
      <ORU_R01.OBSERVATION>
        <OBX>
          ...
        </OBX>
        <ZDR>
          ...
        </ZDR>
      </ORU_R01.OBSERVATION>
    </ORU_R01.ORDER_OBSERVATION>
  </ORU_R01.RESPONSE>
</ORU_R01>

What I don't understand is why are the PID, ORC, OBR, OBX and ZDR segments encoded inside an ORU_R01.RESPONSE, and how do I access those segments from the IMessage?

[milkshakeuk]

Have you had a look at the wiki for examples on how to decode messages?

https://github.com/nHapiNET/nHapi/wiki/Decoding-a-message