Custom SearchParameter tutorial

To create a SearchParameter, FHIRSchema must be enabled (enabled by default)

Objectives

• Understand what SearchParameter is

• Learn how to create a custom SearchParameter in Aidbox

Before you begin

• See what FHIR Search is here, what SearchParameter is here

• Set up the local Aidbox instance using the getting started guide

Get any SearchParameter definition

In AidboxUI, go to FHIR Packages -> hl7.fhir.r4.core and click on "SearchParameters" tab:

Getting all Patient SearchParameters from r4:

Clicking on Patient-active SearchParameter gives us an actual definition of it:

{
  "url": "http://hl7.org/fhir/SearchParameter/Patient-active",
  "id": "Patient-active",
  "base": [
    "Patient"
  ],
  "expression": "Patient.active",
  "name": "active",
  "status": "draft",
  "type": "token",
  "version": "4.0.1",
  "resourceType": "SearchParameter",
  "code": "active",
  "description": "Whether the patient record is active"
}

You can read more about all these fields in SearchParameter fields

The main things:

• change url and id to identify your search parameter

• the code is actual name that is used in the search query

• make sure base is correct

• to define how to search and what to search, type and expression fields are used

• xpathUsage and xpath are ignored

Define a custom SearchParameter

Let's define a custom search parameter that allows searching Patient resources by a specific extension with "http://example.org/fhir/StructureDefinition/occupation" URL:

POST /fhir/SearchParameter
Content-Type: application/json
Accept: application/json

{
  "resourceType": "SearchParameter",
  "id": "patient-occupation",
  "url": "http://example.org/fhir/SearchParameter/patient-occupation",
  "version": "1.0.0",
  "name": "occupation",
  "status": "active",
  "description": "Search patients by occupation",
  "code": "occupation",
  "base": [
    "Patient"
  ],
  "type": "string",
  "expression": "Patient.extension.where(url='http://example.org/fhir/StructureDefinition/occupation').value.as(string)"
}

Here, the main fields are type and expression. String type means that we search for strings in a case-insensitive, accent-insensitive way. See also Search Parameter Types

The expression field uses FHIRPath and defines that we search in "extension" field, filter all the extensions by the URL, and get their value. Note that we use .as(string) to match the string extension choice type.

You can find all SearchParameters created by you in app.aidbox.main package:

Test Search Parameter

Create a Patient resource with the required extension:

POST /fhir/Patient
content-type: application/json
accept: application/json

{
    "resourceType": "Patient",
    "id": "example-patient",
    "extension": [
        {
            "url": "http://example.org/fhir/StructureDefinition/occupation",
            "valueString": "Engineer"
        }
    ],
    "name": [
        {
            "family": "Doe",
            "given": [
                "John"
            ]
        }
    ],
    "gender": "male",
    "birthDate": "1980-01-01"
}

Search for Patient by occupation:

GET /fhir/Patient?occupation=Engin

Response:

Status: 200

resourceType: Bundle
type: searchset
meta:
  versionId: '0'
total: 1
link:
  - relation: first
    url: https://example.aidbox.app/fhir/Patient?occupation=Engin&page=1
  - relation: self
    url: https://example.aidbox.app/fhir/Patient?occupation=Engin&page=1
entry:
  - resource:
      name:
        - given:
            - John
          family: Doe
      gender: male
      birthDate: '1980-01-01'
      extension:
        - url: http://example.org/fhir/StructureDefinition/occupation
          valueString: Engineer
      id: >-
        example-patient
      resourceType: Patient
      meta:
        lastUpdated: '2024-06-07T10:21:29.110510Z'
        versionId: '6'
        extension:
          - url: https://fhir.aidbox.app/fhir/StructureDefinition/created-at
            valueInstant: '2024-06-07T10:21:29.110510Z'
    search:
      mode: match
    fullUrl: https://example.aidbox.app/Patient/example-patient
    link:
      - relation: self
        url: https://example.aidbox.app/Patient/example-patient

More examples

Composite SearchParameter

POST /fhir/SearchParameter
content-type: application/json
accept: application/json

{
  "url": "http://mycompany.com/Questionnaire-context-type-value-ref",
  "component": [
    {
      "definition": "http://hl7.org/fhir/SearchParameter/Questionnaire-context-type",
      "expression": "code"
    },
    {
      "definition": "http://mycompany.com/Questionnaire-context-ref",
      "expression": "value.as(Reference)"
    }
  ],
  "id": "Questionnaire-context-type-value",
  "base": [
    "Questionnaire"
  ],
  "expression": "Questionnaire.useContext",
  "name": "context-type-value",
  "status": "draft",
  "multipleOr": false,
  "type": "composite",
  "version": "4.0.1",
  "xpathUsage": "normal",
  "resourceType": "SearchParameter",
  "code": "context-type-value-ref",
  "description": "A use context type and reference value assigned to the questionnaire"
}