The $viewdefinition-run operation applies a ViewDefinition to transform FHIR resources into a tabular format and returns the results synchronously.

Use Cases:

• Interactive development and debugging of ViewDefinitions
• Real-time data streaming and transformation

FHIR Versions:

Operation may work in FHIR R4 compatibility mode or in R6 mode. In R4 mode, operation can only be on system level ( {BaseURl}/$viewdefinition-run ), for R6 mode operation can appear on type and instance level ({BaseURl}/ViewDefinition/$viewdefinition-run and {BaseURl}/ViewDefinition/{id}/$viewdefinition-run).

Endpoints:

URL: [base]/$viewdefinition-run

URL: [base]/CanonicalResource/$viewdefinition-run

URL: [base]/CanonicalResource/[id]/$viewdefinition-run

Parameters

HTTP Methods

• GET: For simple invocations without request body
• POST: Required when providing ViewDefinition resource or resources to transform

GET Method Limitations

When using the GET method, the following limitations apply:

1. No Request Body Parameters: GET requests cannot include parameters that require a request body:
   • Cannot provide viewResource parameter (inline ViewDefinition)
   • Cannot provide resource parameter (direct resources to transform)
2. Available Parameters: Only parameters that can be passed as query parameters are supported:
   • _format - Output format specification
   • header - Include CSV headers (for CSV format)
   • patient - Filter by patient reference
   • group - Filter by group membership
   • _since - Filter by last updated time
   • _limit - Limit number of result rows
   • source - External data source
3. Use Cases: GET is suitable for:
   • Instance-level invocations where the ViewDefinition is identified by the URL path
   • Simple filtering and formatting of server data
   • Quick queries without complex configuration
4. When POST is Required: Use POST instead of GET when you need to:
   • Provide an inline ViewDefinition via viewResource parameter
   • Supply resources directly via resource parameter for transformation
   • Pass complex parameter values that cannot be represented as query strings

Data Sources

The operation can process data from:

1. Direct resources - Provided via resource parameter in the request
2. Server resources - From the server’s data store (default)
3. External source - Specified via source parameter

Request Format

Output Format

This operation uses the shared output-format enumeration (json, ndjson, csv, parquet, fhir), content-negotiation rules, and return-representation rules defined once in Common Operation Behavior. Only a summary is repeated here.

The format is selected by (in order of precedence):

• _format parameter: shortened format names (json, ndjson, csv, parquet, fhir)
• Accept header: standard MIME types (application/json, application/x-ndjson, text/csv, application/octet-stream, application/fhir+json)

Examples:

• _format=json or Accept: application/json
• _format=ndjson or Accept: application/x-ndjson
• _format=csv or Accept: text/csv
• _format=parquet or Accept: application/octet-stream
• _format=fhir or Accept: application/fhir+json

The Accept header also governs a second, independent axis — whether the body is the raw payload (the default) or a serialized Binary resource envelope. See Content Negotiation.

Filtering

Optional filtering parameters:

• patient - Filter by patient reference
• group - Filter by group membership
• _since - Filter by last updated time
• _limit - Limit number of result rows

Response Format

• Success (200 OK): Returns the raw payload in the requested format, with Content-Type set to the format’s native media type (not a serialized Binary envelope unless a FHIR media type is requested — see Return Representation)
• Error (4xx/5xx): Returns OperationOutcome resource
• Transfer framing: The response of any format MAY use Transfer-Encoding: chunked. Chunked transfer is an HTTP transport choice, independent of the format; it is distinct from incremental result production. See Streaming and Transfer Encoding
• JSON format: Returns an array of objects

Parameters

Input Parameters

Core Parameters

¹ Either viewReference or viewResource is required at type level; neither allowed at instance level

Output Control

Filtering

Data Source

Output Parameter

View Reference/Resource Clarification

Only one of the viewReference or viewResource parameters can be provided. When invoking this operation at the instance level (e.g. ViewDefinition/{id}/$run), the server SHALL automatically infer the viewReference parameter from the path parameter.

The viewReference parameter MAY be specified using any of the following formats:

• A relative URL on the server (e.g. “ViewDefinition/123”)

• A canonical URL (e.g. “http://specification.org/fhir/ViewDefinition/123

  1.0.0”)

• An absolute URL (e.g. “http://example.org/fhir/ViewDefinition/123”)

Servers MAY choose which reference formats they support. Servers SHALL document which reference formats they support in their CapabilityStatement.

For servers that want to support all types of references, it is recommended to use the following algorithm:

1. If the reference is a relative URL, resolve it on the server side.
2. If the reference is an absolute URL, look up the available server Artifact registry for a resource with the same canonical URL and version if provided.
3. Otherwise, try to load the ViewDefinition from the provided absolute URL.

Format Parameter Clarification

The supported formats (json, ndjson, csv, parquet, fhir), the default, the Accept-vs-_format precedence rule, and the optional fhir shape are defined in Common Operation Behavior and apply to this operation:

• It is RECOMMENDED to support json, ndjson and csv by default; servers MAY support parquet and fhir, and SHALL document supported formats in the CapabilityStatement.
• If _format is omitted (and no format is derivable from Accept), the server SHALL return the result in ndjson format.
• When _format is supplied, its value SHALL take precedence over Accept.
• _format=fhir returns a Parameters resource with one repeating row per result row, using the SQL to FHIR type mapping.

Patient Parameter Clarification

When provided, the server SHALL NOT return resources in the patient compartments belonging to patients outside of this list.

If a client requests patients who are not present on the server, the server SHOULD return details via a FHIR OperationOutcome resource in an error response to the request.

Group Parameter Clarification

When provided, the server SHALL NOT return resources that are not a member of the supplied Group.

If a client requests groups that are not present on the server, the server SHOULD return details via a FHIR OperationOutcome resource in an error response to the request.

Since Parameter Clarification

Resources will be included in the response if their state has changed after the supplied time (e.g., if Resource.meta.lastUpdated is later than the supplied _since time). In the case of a Group level export, the server MAY return additional resources modified prior to the supplied time if the resources belong to the patient compartment of a patient added to the Group after the supplied time (this behavior SHOULD be clearly documented by the server). For Patient- and Group-level requests, the server MAY return resources that are referenced by the resources being returned regardless of when the referenced resources were last updated. For resources where the server does not maintain a last updated time, the server MAY include these resources in a response irrespective of the _since value supplied by a client.

Resource Parameter and Bundle Inputs

The resource parameter is repeatable and carries the discrete FHIR resources to transform instead of using server data. Because a Bundle is itself a Resource, a Bundle satisfies the parameter’s Resource type. To avoid ambiguity, the following rule applies:

When a resource value is a Bundle, the server SHALL unwrap it and run the ViewDefinition against each Bundle.entry[*].resource, exactly as if those entries had been supplied as individual repeated resource values. The Bundle itself is not treated as an input resource for the ViewDefinition.

Unwrapping is applied one level deep. Resources within the bundle are evaluated against the ViewDefinition’s resource type just like directly supplied resources: entries whose type does not match the ViewDefinition’s resource are ignored. Mixing discrete resource values and Bundle values in the same request is permitted; the effective input is the union of the discrete resources and every unwrapped bundle entry.

Examples

Successful Requests

Example 1: Instance-level GET with CSV output

GET /ViewDefinition/patient-demographics/$run HTTP/1.1
Accept: text/csv

HTTP/1.1 200 OK
Content-Type: text/csv
Transfer-Encoding: chunked

id,birthDate,family,given
pt-1,1990-01-15,Smith,John
pt-2,1985-03-22,Johnson,Mary
pt-3,1992-07-08,Williams,Robert

Example 2: Type-level POST with inline ViewDefinition

POST /ViewDefinition/$run HTTP/1.1
Accept: application/json
Content-Type: application/fhir+json

{
  "resourceType": "Parameters",
  "parameter": [{
    "name": "viewResource",
    "resource": {
      "resourceType": "ViewDefinition",
      "resource": "Patient",
      "select": [{
        "column": [
          {"name": "id", "type": "id", "path": "getResourceKey()"},
          {"name": "birthDate", "type": "date", "path": "birthDate"},
          {"name": "family", "type": "string", "path": "name.family"},
          {"name": "given", "type": "string", "path": "name.given"}
        ]
      }]
    }
  }]
}

HTTP/1.1 200 OK
Content-Type: application/json

[
  {"id": "pt-1", "birthDate": "1990-01-15", "family": "Smith", "given": "John"},
  {"id": "pt-2", "birthDate": "1985-03-22", "family": "Johnson", "given": "Mary"},
  {"id": "pt-3", "birthDate": "1992-07-08", "family": "Williams", "given": "Robert"}
]

Example 3: POST with direct resources

POST /ViewDefinition/$run HTTP/1.1
Accept: text/csv
Content-Type: application/fhir+json

{
  "resourceType": "Parameters",
  "parameter": [{
    "name": "viewResource",
    "resource": {
      "resourceType": "ViewDefinition",
      "resource": "Patient",
      "select": [{
        "column": [
          {"name": "id", "type": "id", "path": "getResourceKey()"},
          {"name": "birthDate", "type": "date", "path": "birthDate"},
          {"name": "family", "type": "string", "path": "name.family"},
          {"name": "given", "type": "string", "path": "name.given"}
        ]
      }]
    }
  },
  {
    "name": "resource",
    "resource": {
      "resourceType": "Patient",
      "id": "pt-1",
      "name": [{
        "use": "official",
        "family": "Cole",
        "given": ["Joanie"]
      }],
      "birthDate": "2012-03-30"
    }
  },
  {
    "name": "resource",
    "resource": {
      "resourceType": "Patient",
      "id": "pt-2",
      "name": [{
        "use": "official",
        "family": "Doe",
        "given": ["John"]
      }],
      "birthDate": "2012-03-30"
    }
  }]
}

HTTP/1.1 200 OK
Content-Type: text/csv

id,birthDate,family,given
pt-1,2012-03-30,Cole,Joanie
pt-2,2012-03-30,Doe,John

Example 4: GET with filters

GET /ViewDefinition/encounters/$run?patient=Patient/123&_limit=10&_format=ndjson HTTP/1.1

HTTP/1.1 200 OK
Content-Type: application/x-ndjson
Transfer-Encoding: chunked

{"id":"enc-1","patient":"Patient/123","status":"finished","class":"ambulatory","period_start":"2023-01-15T10:00:00Z"}
{"id":"enc-2","patient":"Patient/123","status":"finished","class":"emergency","period_start":"2023-02-20T14:30:00Z"}
{"id":"enc-3","patient":"Patient/123","status":"in-progress","class":"inpatient","period_start":"2023-03-01T08:00:00Z"}

Example 5: POST with a Bundle of resources

A Bundle supplied as a resource value is unwrapped; the ViewDefinition runs against each entry. This request is equivalent to Example 3, which passed the two Patients as discrete resource values.

POST /ViewDefinition/$run HTTP/1.1
Accept: text/csv
Content-Type: application/fhir+json

{
  "resourceType": "Parameters",
  "parameter": [{
    "name": "viewResource",
    "resource": {
      "resourceType": "ViewDefinition",
      "resource": "Patient",
      "select": [{
        "column": [
          {"name": "id", "type": "id", "path": "getResourceKey()"},
          {"name": "birthDate", "type": "date", "path": "birthDate"},
          {"name": "family", "type": "string", "path": "name.family"},
          {"name": "given", "type": "string", "path": "name.given"}
        ]
      }]
    }
  },
  {
    "name": "resource",
    "resource": {
      "resourceType": "Bundle",
      "type": "collection",
      "entry": [
        { "resource": { "resourceType": "Patient", "id": "pt-1", "name": [{"family": "Cole", "given": ["Joanie"]}], "birthDate": "2012-03-30" } },
        { "resource": { "resourceType": "Patient", "id": "pt-2", "name": [{"family": "Doe", "given": ["John"]}], "birthDate": "2012-03-30" } }
      ]
    }
  }]
}

HTTP/1.1 200 OK
Content-Type: text/csv

id,birthDate,family,given
pt-1,2012-03-30,Cole,Joanie
pt-2,2012-03-30,Doe,John

Error Handling

HTTP Status Codes

The operation uses standard HTTP status codes to indicate the outcome:

All error responses (4xx and 5xx) SHOULD include an OperationOutcome resource providing details about the error.

Common Error Scenarios

1. Unsupported Parameters

When the server does not support certain parameters, it should return 400 Bad Request:

GET /ViewDefinition/123/$run?_since=2021-01-01 HTTP/1.1
Accept: application/json

HTTP/1.1 400 Bad Request
Content-Type: application/fhir+json

{
  "resourceType": "OperationOutcome",
  "issue": [
    {
      "severity": "error",
      "code": "not-supported",
      "diagnostics": "The server does not support the _since parameter",
      "expression": ["_since"]
    }
  ]
}

2. Invalid ViewDefinition

When the provided ViewDefinition is invalid, return 422 Unprocessable Entity:

POST /ViewDefinition/$run HTTP/1.1
Content-Type: application/fhir+json
Accept: application/json

{
  "resourceType": "Parameters",
  "parameter": [{
    "name": "viewResource",
    "resource": {
      "resourceType": "ViewDefinition",
      "resource": "Patient",
      "select": [{
        "column": [
          {"name": "id", "path": "invalid.path.syntax"}
        ]
      }]
    }
  }]
}

HTTP/1.1 422 Unprocessable Entity
Content-Type: application/fhir+json

{
  "resourceType": "OperationOutcome",
  "issue": [
    {
      "severity": "error",
      "code": "invalid",
      "diagnostics": "The ViewDefinition is invalid: column 'id' contains invalid FHIRPath expression",
      "expression": ["viewResource.select[0].column[0].path"]
    }
  ]
}

3. ViewDefinition Not Found

When the referenced ViewDefinition does not exist:

GET /ViewDefinition/non-existent/$run HTTP/1.1
Accept: application/json

HTTP/1.1 404 Not Found
Content-Type: application/fhir+json

{
  "resourceType": "OperationOutcome",
  "issue": [
    {
      "severity": "error",
      "code": "not-found",
      "diagnostics": "ViewDefinition with id 'non-existent' not found"
    }
  ]
}

4. Missing Required Parameters

When required parameters are missing:

POST /ViewDefinition/$run HTTP/1.1
Content-Type: application/fhir+json
Accept: text/csv

{
  "resourceType": "Parameters",
  "parameter": []
}

HTTP/1.1 400 Bad Request
Content-Type: application/fhir+json

{
  "resourceType": "OperationOutcome",
  "issue": [
    {
      "severity": "error",
      "code": "required",
      "diagnostics": "Either viewReference or viewResource parameter is required when invoking at type level"
    }
  ]
}

5. Invalid Format

When an unsupported format is requested:

GET /ViewDefinition/123/$run?_format=xml HTTP/1.1

HTTP/1.1 400 Bad Request
Content-Type: application/fhir+json

{
  "resourceType": "OperationOutcome",
  "issue": [
    {
      "severity": "error",
      "code": "not-supported",
      "diagnostics": "Format 'xml' is not supported. Supported formats: json, ndjson, csv, parquet, fhir",
      "expression": ["_format"]
    }
  ]
}

6. Patient Not Found

When filtering by a patient that doesn’t exist:

GET /ViewDefinition/lab-results/$run?patient=Patient/non-existent HTTP/1.1
Accept: application/json

HTTP/1.1 400 Bad Request
Content-Type: application/fhir+json

{
  "resourceType": "OperationOutcome",
  "issue": [
    {
      "severity": "error",
      "code": "not-found",
      "diagnostics": "Patient with id 'non-existent' not found",
      "expression": ["patient"]
    }
  ]
}

7. Resource Processing Errors

When errors occur during data transformation:

HTTP/1.1 500 Internal Server Error
Content-Type: application/fhir+json

{
  "resourceType": "OperationOutcome",
  "issue": [
    {
      "severity": "error",
      "code": "processing",
      "diagnostics": "Error processing Patient/123: Required field 'birthDate' is missing",
      "expression": ["resource[2]"]
    }
  ]
}