Search

Pathling extends the search capabilities of FHIR using FHIRPath expressions for filtering. This allows you to retrieve a set of FHIR resources from the server filtered by one or more FHIRPath expressions.

Each expression is evaluated against each resource, returning a Boolean value which determines whether the resource will be included in the search result.

This is implemented as a named query called fhirPath. Multiple instances of the filter parameter are combined using Boolean AND logic, and multiple expressions can be provided within a single parameter and delimited by commas to achieve OR logic. In addition to this, FHIRPath boolean operators can be used within expressions.

GET [FHIR endpoint]/[resource type]?_query=fhirPath&filter=[FHIRPath expression]...

POST [FHIR endpoint]/[resource type]/_search

Request

The filter parameter is used to specify FHIRPath expressions:

• filter [1..*] - (string) A FHIRPath expression that can be evaluated against each resource in the data set to determine whether it is included within the result. The context is an individual resource of the type that the search is being invoked against. The expression must evaluate to a Boolean value.

Parameters are passed in the query portion of the URL for GET requests, and can be passed either in the URL or in an application/x-www-form-urlencoded body for POST requests.

Response

Any search request in FHIR returns a Bundle of matching resources.

Pagination links are included for responses which include a large number of resources. The number of resources returned in a single response is 100 by default — this can be altered using the _count parameter.

See Search in the FHIR specification for more details.

Example response:

{
    "resourceType": "Bundle",
    "type": "searchset",
    "total": 2,
    "link": [
        {
            "relation": "self",
            "url": "http://localhost:8080/fhir/Patient?_query=fhirPath&filter=gender%3D'male'"
        }
    ],
    "entry": [
        {
            "resource": {
                "resourceType": "Patient",
                "id": "patient-1",
                "gender": "male",
                "birthDate": "1970-01-01"
            }
        },
        {
            "resource": {
                "resourceType": "Patient",
                "id": "patient-2",
                "gender": "male",
                "birthDate": "1985-06-15"
            }
        }
    ]
}

Examples

Simple filter

Retrieve all male patients:

GET /fhir/Patient?_query=fhirPath&filter=gender%3D'male'

This is the URL-encoded form of gender='male'.

AND logic

Retrieve female patients who are active (multiple filter parameters):

GET /fhir/Patient?_query=fhirPath&filter=gender%3D'female'&filter=active%3Dtrue

This is the URL-encoded form of gender='female' and active=true.

OR logic

Retrieve patients who are either male or female (comma-separated within single parameter):

GET /fhir/Patient?_query=fhirPath&filter=gender%3D'male'%2Cgender%3D'female'

This is the URL-encoded form of gender='male',gender='female'.

Complex expressions

Retrieve patients born after 1980:

GET /fhir/Patient?_query=fhirPath&filter=birthDate%20%3E%20%401980-01-01

This is the URL-encoded form of birthDate > @1980-01-01.

Using FHIRPath operators

Retrieve observations with a specific code and value above threshold:

GET /fhir/Observation?_query=fhirPath&filter=code.coding.code%3D'8867-4'%20and%20valueQuantity.value%20%3E%20100

This is the URL-encoded form of code.coding.code='8867-4' and valueQuantity.value > 100.