13.17.1Working with DuplicatesExperimental
FHIR Repositories can end up with duplicate resources in them. This page details tools that Smile provides to work with duplicated data.
| Cause of Duplicates | Recommended Approach |
|---|---|
| The same entities were imported from different source systems. E.g. Jane Smith's Patient record is imported from the Lab system as Patient/123 and from the Pharmacy system as Patient/456. | Preserve the source data as is so that future data continues to be properly associated to the right patients. Use MDM to establish Golden Resources and MDM LINK records outside of the data and use MDM features like Observation?patient=Patient/123&_mdm=true to link the data at search time. |
| Data was accidentally duplicated on import. E.g. the same data was accidentally loaded twice (as POST new resources) or Conditional Create directives failed to match the intended target correctly. This kind of unintended duplication can also occur when translating HL7v2, CDA, or CSV data into FHIR resources. | In the case where the data was accidentally duplicated, it may make sense to "clean up" the duplicates. See below for details on Smile CDR tools to merge such duplicates. |
13.17.1.1Deduplication Operations
Smile CDR provides two operations to deduplicate data:
$mergewhich is a backport of the FHIR R5 Patient/$merge specification to FHIR R4$hapi.fhir.replace-referencesperforms only the update references part of this$mergeoperation.
13.17.1.1.1`$merge` Operation
See the FHIR R5 Patient/$merge specification page for a description of this operation. See the bottom of this page for details on the current roadmap for enhancing Smile CDR deduplication functionality.
13.17.1.1.1.1`$merge` Input Parameters
| Name | Type | Default | Notes |
|---|---|---|---|
| source-patient-identifier | Identifier | List of source patient identifiers | |
| source-patient | Reference | Source patient | |
| target-patient-identifier | Identifier | List of target patient identifiers | |
| target-patient | Reference | Target patient | |
| result-patient | Patient | Optional merged patient resource | |
| preview | Boolean | false | If true, no changes will be made and response will summarize what would happen were the merge to occur |
| delete-source | Boolean | false | If true, delete the source resource |
| resource-limit | Integer | 512 | If the request is synchrononous and the number of resources to change exceeds this threshold, the operation will fail with 412 Precondition Failed. This parameter has no effect if the Prefer: respond-async header is set |
See the FHIR R5 Patient/$merge specification for a detailed description of these input parameters.
resource-limit is a Smile CDR addition to protect users from accidentally changing too many resources at once. If resource-limit is larger than 10000, the value 10000 will be used.
If you request that the operation be performed asynchronously by providing the Prefer: respond-async HTTP header, then the resource-limit parameter is ignored.
When performed asynchronously, the operation is performed in batches of 1024 resource patches at a time, via PATCH transaction transaction Bundles.
13.17.1.1.1.2`$merge` Output Parameters
| Name | Type | Notes |
|---|---|---|
| input | Parameters | A copy of the input parameters used in the $merge operation |
| outcome | OperationOutcome | Details about the result of the merge |
| result | Patient | The merged Patient resource |
| task | Task | If the merge operation was performed asynchronously, this Task resource provides details about the status of the merge operation |
13.17.1.1.1.3Merge Provenance Resource
With the 2025.08 release, the $merge operation creates a Provenance resource upon successful completion.
This Provenance resource contains, in its target element, the versioned references to the target patient,
the source patient (if not deleted during the operation), and all other resources updated as part of the operation.
The Provenance.activity is set to http://terminology.hl7.org/CodeSystem/iso-21089-lifecycle|merge, and the Provenance.agent.who is populated with a logical reference to the request user.
13.17.1.1.1.4Merge Example 1: Merge Patient/2 into Patient/3 synchronously.
Input:
POST /Patient/$merge
Content-Type: application/fhir+json
{
"resourceType": "Parameters",
"parameter": [
{
"name": "source-patient",
"valueReference": {
"reference": "Patient/2"
}
},
{
"name": "target-patient",
"valueReference": {
"reference": "Patient/3"
}
}
]
}
Output:
HTTP/1.1 200 OK
{
"resourceType": "Parameters",
"parameter": [
{
"name": "input",
"resource": {
"resourceType": "Parameters",
"parameter": [
{
"name": "source-patient",
"valueReference": {
"reference": "Patient/2"
}
},
{
"name": "target-patient",
"valueReference": {
"reference": "Patient/3"
}
}
]
}
},
{
"name": "outcome",
"resource": {
"resourceType": "OperationOutcome",
"issue": [
{
"severity": "information",
"details": {
"text": "Merge operation completed successfully."
}
}
]
}
},
{
"name": "result",
"resource": {
"resourceType": "Patient",
"id": "3",
"identifier": [
{
"system": "SYS2A",
"value": "VAL2A"
},
{
"system": "SYS2B",
"value": "VAL2B"
},
{
"system": "SYSC",
"value": "VALC"
},
{
"use": "old",
"system": "SYS1A",
"value": "VAL1A"
},
{
"use": "old",
"system": "SYS1B",
"value": "VAL1B"
}
],
"link": [
{
"other": {
"reference": "Patient/2"
},
"type": "replaces"
}
]
}
}
]
}
13.17.1.1.1.5Merge Example 2: Preview merge Patient/2 into Patient/3 synchronously.
Input:
POST /Patient/$merge
Content-Type: application/fhir+json
{
"resourceType": "Parameters",
"parameter": [
{
"name": "source-patient",
"valueReference": {
"reference": "Patient/2"
}
},
{
"name": "target-patient",
"valueReference": {
"reference": "Patient/3"
}
},
{
"name": "preview",
"valueBoolean": "true"
}
]
}
Output:
HTTP/1.1 200 OK
{
"resourceType": "Parameters",
"parameter": [
{
"name": "input",
"resource": {
"resourceType": "Parameters",
...copy of input...
}
},
{
"name": "outcome",
"resource": {
"resourceType": "OperationOutcome",
"issue": [
{
"severity": "information",
"details": {
"text": "Preview only merge operation - no issues detected"
},
"diagnostics": "Merge would update 25 resources"
}
]
}
},
{
"name": "result",
"resource": {
"resourceType": "Patient",
...merged patient...
}
}
]
}
13.17.1.1.1.6Merge Example 3: Merging Patients by identifier asynchronously.
Input:
POST /Patient/$merge
Content-Type: application/fhir+json
Prefer: respond-async
{
"resourceType": "Parameters",
"parameter": [ {
"name": "source-patient-identifier",
"valueIdentifier": {
"system" : "urn:oid:1.2.36.146.595.217.0.1",
"value" : "12345"
}
},
{
"name": "target-patient-identifier",
"valueIdentifier": {
"system" : "urn:oid:1.2.36.146.595.217.0.1",
"value" : "12346"
}
}
]
}
Output:
HTTP/1.1 202 Accepted
{
"resourceType": "Parameters",
"parameter": [
{
"name": "input",
"resource": {
"resourceType": "Parameters",
...copy of input...
}
},
{
"name": "task",
"resource": {
"resourceType": "Task",
"id": "352",
"identifier": [
{
"system": "http://hapifhir.io/batch/jobId",
"value": "26738f4d-266c-4ef6-934f-1d13b1b474b9"
}
],
"status": "in-progress"
}
}
]
}
You can poll the status of the returned Task resource see when it completes. For more detailed status about the background job, you can view the status of the corresponding Smile CDR batch job either through the Web Admin Console, or through the Admin JSON API. The id of the Smile CDR batch job is provided as an identifer on the returned Task.
13.17.1.1.2`$hapi.fhir.replace-references` Operation
The $hapi.fhir.replace-references operation searches for all resources in the repository that have a reference to the
source resource, and updates those references to point to the target resource. It is a simplified form of the $merge operation when all you want to do is update references.
This operation creates a Transaction Bundle of Patch operations to update the references and returns the output of performing that transaction.
13.17.1.1.2.1`$hapi.fhir.replace-references` Input Parameters
| Name | Type | Default | Notes |
|---|---|---|---|
| source-reference-id | String | The id of the source resource reference to be replaced | |
| target-reference-id | String | The id of the target resource reference that the references will be replaced with | |
| resource-limit | Integer | 512 | If the request is synchrononous and the number of resources to change exceeds this threshold, the operation will fail with 412 Precondition Failed. This parameter has no effect if the Prefer: respond-async header is set |
The resource-limit parameter is available to control how many resources can be changed by this operation. If resource-limit is larger than 10000, the value 10000 will be used.
If you request that the operation be performed asynchronously by providing the Prefer: respond-async HTTP header, then the resource-limit parameter is ignored.
When performed asynchronously, the operation is performed in batches of 1024 resource patches at a time, via PATCH transaction transaction Bundles.
13.17.1.1.2.2`$hapi.fhir.replace-references` Output Parameters
| Name | Type | Notes |
|---|---|---|
| outcome | Bundle | The result of the Bundle patch transaction |
| task | Task | If the operation was performed asynchronously, this Task resource provides details about the status of the operation |
See the $merge operation above for details about the returned Task resource in the case when the operation is performed asynchronously.
13.17.1.1.2.3Replace References Provenance Resource
With the 2025.08 release, the $hapi.fhir.replace-references operation creates a Provenance resource upon successful completion. This Provenance resource contains, in its target element, the versioned references to the target resource,
the source resource, and the resources updated as part of the operation.
The Provenance.activity is set to http://terminology.hl7.org/CodeSystem/iso-21089-lifecycle|link, and the Provenance.agent.who is populated with a logical reference to the request user.
13.17.1.1.2.4Replace References Example: Replace all references to Patient/2 with references to Patient/3 synchronously.
Input:
POST /Patient/$merge
Content-Type: application/fhir+json
{
"resourceType": "Parameters",
"parameter": [
{
"name": "source-reference-id",
"valueString": "Patient/2"
},
{
"name": "target-reference-id",
"valueString": "Patient/3"
}
]
}
Output:
HTTP/1.1 200 OK
{
"resourceType": "Parameters",
"parameter": [
{
"name": "outcome",
"resource": {
"resourceType": "Bundle",
"id": "782add05-549c-4a7e-a687-38c22f2f12d0",
"type": "transaction-response",
"entry": [
{
"response": {
"status": "200 OK",
"location": "CarePlan/62/_history/2",
"etag": "2",
"outcome": {
"resourceType": "OperationOutcome",
"issue": [
{
"severity": "information",
"code": "informational",
"details": {
"coding": [
{
"system": "https://hapifhir.io/fhir/CodeSystem/hapi-fhir-storage-response-code",
"code": "SUCCESSFUL_PATCH",
"display": "Patch succeeded."
}
]
},
"diagnostics": "Successfully patched resource \"CarePlan/62/_history/2\"."
}
]
}
}
},
... etc outcome of the rest of the patch operations ...
]
}
}
}
}
13.17.1.2Deduplication Roadmap
The Deduplication features of Smile CDR are under active development. Here is a roadmap of new features we are planning to roll out.
13.17.1.2.1Feb 2025 Release
- Implement Provenance part of the Patient/$merge specification for both
$mergeand$hapi.fhir.replace-references - Extend
$mergeto all Resource types
13.17.1.2.2May or Aug 2025 Release
- Create new
$undo-mergeand$hapi.fhir.undo-replace-referencesoperations that use the Provenance resources to undo the effects of those operations (assuming that none of the affected resources have subsequentially changed).
13.17.1.2.3Sometime after the May 2025 Release
- Create a third MDM mode:
MATCH_AND_MERGEwhich is similar toMATCH_ONLYin that it uses MDM Rules but does not create any links or Golden Resources. When enabled, aMATCH_AND_MERGEMDM module will automatically perform a$mergeoperation on all inbound resources. Any resources that MATCH a single target will be merged into that resources following the MDM Survivorship rules and all references will be updated to point to the merged resource. - Create a new
$deduplicateoperation that takes a FHIR Bundle resource as input and uses MDM Rules to remove duplicates from the inbound Bundle and update references to point to the matched resource. Think of this as a stronger version of Conditional Create where you now have the full power of MDM matching to find matching resources rather than being limited by the FHIR Conditional Create syntax. - Provide this new
$deduplicateoperation as a Camel Processor - Provide a new
$submit-for-deduplicationoperation that works like$mdm-submitand performs MATCH_AND_MERGE on all resources that match the criteria in the request. E.g. If Organization resources with_source=ABCwere accidentally duplicated in your FHIR Repository, you could call$submit-for-deduplicationwith the criteriaOrganization?_source=ABCto submit all of those Organizations for deduplication. Ones that have existing matches would be deleted and all references updated to point to the remaining copy of that organization.