Assembling Fhir Bundles

Assembling FHIR Bundles

A FHIR server ingests one transaction Bundle, not loose resources, and the resources inside it must cross-reference each other (Condition.subject → Patient, Observation.encounter → Encounter, DiagnosticReport.result → Observation). OpenMed ships a deterministic, mechanical Bundle assembler — openmed.clinical.exporters.fhir.to_bundle — that wraps the resources you built in exporting-to-fhir into a valid R4 Bundle and wires up the references.

When to use

Use after you have a list of standalone resources from exporting-to-fhir and the destination is a FHIR server. Reach for it when the user says "build a Bundle", "transaction", "POST these resources", or needs internal references resolved. To check the Bundle against US Core, hand off to validating-us-core.

What OpenMed gives you (verified API)

from openmed.clinical.exporters.fhir import to_bundle, deterministic_fullurl

bundle = to_bundle(
    resources,                       # Sequence[Mapping] each with a resourceType
    doc_id="note-2024-03-02-001",    # seeds stable urn:uuid fullUrls
    bundle_type="transaction",       # "transaction" | "batch" | "collection" | ...
)

to_bundle does exactly three things, and never synthesises or validates:

1. Deterministic fullUrl. Each resource gets a urn:uuid seeded by doc_id + its index, so the same input always produces byte-identical output (golden-test friendly). You can pre-compute the same urn with deterministic_fullurl(doc_id, index).
2. Reference rewriting. Any {"reference": "ResourceType/id"} whose target is present in the Bundle is repointed at that resource's fullUrl. References to resources absent from the Bundle (e.g. a Patient removed by de-identification) are left untouched — no dangling internal refs.
3. Request blocks. For transaction/batch bundles each entry gets a request block ({"method": "POST", "url": "<ResourceType>"}) so the server knows to create it.

It raises ValueError if a resource lacks resourceType, or if two resources share the same ResourceType/id (duplicate ids would silently corrupt the reference map).

Quick start

from openmed.clinical.exporters.fhir import to_bundle
from openmed.clinical.exporters.codeable_concept_simple import coding, codeable_concept

condition = {
    "resourceType": "Condition", "id": "cond-1",
    "clinicalStatus": {"coding": [{
        "system": "http://terminology.hl7.org/CodeSystem/condition-clinical",
        "code": "active"}]},
    "code": codeable_concept(
        [coding("snomed", "44054006", "Diabetes mellitus type 2")],
        text="type 2 diabetes"),
    "subject": {"reference": "Patient/patient-1"},   # internal ref, rewritten
}
medication = {
    "resourceType": "MedicationStatement", "id": "med-1", "status": "active",
    "medicationCodeableConcept": codeable_concept(
        [coding("rxnorm", "860975", "metformin 500 MG Oral Tablet")],
        text="metformin 500 mg"),
    "subject": {"reference": "Patient/patient-1"},
}
patient = {
    "resourceType": "Patient", "id": "patient-1",
    "gender": "unknown",                              # de-identified, synthetic
}

bundle = to_bundle([patient, condition, medication],
                   doc_id="demo-note", bundle_type="transaction")

Worked: the transaction Bundle

{
  "resourceType": "Bundle",
  "type": "transaction",
  "entry": [
    {
      "fullUrl": "urn:uuid:6f1c...e2",
      "resource": { "resourceType": "Patient", "id": "patient-1", "gender": "unknown" },
      "request": { "method": "POST", "url": "Patient" }
    },
    {
      "fullUrl": "urn:uuid:9a3b...77",
      "resource": {
        "resourceType": "Condition", "id": "cond-1",
        "subject": { "reference": "urn:uuid:6f1c...e2" }
      },
      "request": { "method": "POST", "url": "Condition" }
    },
    {
      "fullUrl": "urn:uuid:c0d4...19",
      "resource": {
        "resourceType": "MedicationStatement", "id": "med-1",
        "subject": { "reference": "urn:uuid:6f1c...e2" }
      },
      "request": { "method": "POST", "url": "MedicationStatement" }
    }
  ]
}

Note Condition.subject and MedicationStatement.subject were rewritten from "Patient/patient-1" to the Patient entry's fullUrl — that is what makes the transaction resolvable in a single POST.

Workflow

1. Build resources with exporting-to-fhir; give each a unique id.
2. Put any resource you reference inside the same Bundle — including the Patient — so the reference resolves. References to resources you intend to be already on the server (e.g. an existing Patient) are left as literal "Patient/<id>"; resolve those with conditional create (below).
3. Call to_bundle(resources, doc_id=<stable>, bundle_type="transaction").
4. POST the whole Bundle to the server base: POST [base] {Bundle}.
5. Validate first against US Core (validating-us-core).

Conditional create (don't duplicate an existing Patient)

to_bundle writes POST <ResourceType> request blocks. To make a transaction idempotent, post-process the entry's request to add an ifNoneExist query so the server reuses an existing match instead of creating a duplicate:

for entry in bundle["entry"]:
    if entry["resource"]["resourceType"] == "Patient":
        entry["request"]["ifNoneExist"] = "identifier=http://hospital.example|MRN-REDACTED"

The server creates the Patient only if no match exists; otherwise it links the references to the existing one. PUT with a known id is the alternative for true upserts.

Hand-off to / from OpenMed

• From OpenMed: the resource list comes from exporting-to-fhir, which in turn comes from openmed.analyze_text. Keep doc_id stable per source document so re-running the pipeline yields the same Bundle.
• De-identify a built Bundle: openmed.interop.fhir_operations.de_identify_bundle(bundle) walks every entry's free text + XHTML narrative and de-identifies it while preserving Bundle type, entry order, fullUrls, request blocks, and references — codes, systems, and temporal values are never altered. Use it as a final safety pass before transmission if any narrative might carry PHI.
• OperationOutcome: a transaction either fully succeeds or fully fails; the server returns a Bundle of responses (or an OperationOutcome on error). Surface those to the user; for your own pre-flight findings use to_operation_outcome(...) from the same package.

Edge cases & gotchas

• Resources without an id are valid but unreferenceable — nothing can point at them and they will not be reference-rewrite targets.
• Duplicate ResourceType/id raises. This is intentional: a duplicate id would silently overwrite an entry in the reference map and corrupt cross-references. Make ids unique.
• External references are left alone. Only references whose target is in the Bundle are rewritten; a "Patient/existing-123" you mean to resolve on the server stays literal — pair it with ifNoneExist or a PUT.
• transaction vs batch. transaction is atomic (all-or-nothing, server resolves urn:uuid references); batch is independent per-entry and does not guarantee reference resolution. Use transaction when entries reference each other.
• collection/document bundles get no request blocks (only transaction/batch do) — correct, since they are not meant to be POSTed for creation.
• The assembler does not validate profiles. Run validating-us-core before submission.

Standards & references

• FHIR R4 Bundle: https://hl7.org/fhir/R4/bundle.html
• Transactions & batches: https://hl7.org/fhir/R4/http.html#transaction
• Bundle references / fullUrl resolution: https://hl7.org/fhir/R4/bundle.html#references
• Conditional create (ifNoneExist): https://hl7.org/fhir/R4/http.html#cond-update