This page is part of the FHIR Specification (v5.0.0: R5 - STU). This is the current published version in it's permanent home (it will always be available at this URL). For a full list of available versions, see the Directory of published versions
FHIR Infrastructure Work Group | Maturity Level: Normative | Standards Status: Trial use |
The Expression type indicates that one of the allowed languages is application/x-fhir-query
.
This is defined as a FHIR search string. Normally this will not include the base URL and is intended
to be invoked against the server that is in scope (usually based on the base URL of the resource containing the Expression).
However, in some cases, a full URL might be specified, i.e. if the author of the resource wants resources to always be retrieved from a
specific source.
In addition to the base query syntax, this specification allows for the injection of FHIRPath into the query expressions. This allows the
queries to take advantage of context when they are invoked. Systems SHALL evaluate and substitute the results of such queries before executing them.
The FHIRPaths are denoted by surrounding them with double curly-braces (i.e. {{ fhirpath goes here }}
) in the same way expressions are denoted in the
Liquid templating language.
For example:
Observation?code=http://loinc.org|65972-2&date=gt{{today()-7 days}}&subject={{%patient.id}}
would return all Observations with the specified LOINC code made in the last week for the specified patient (the %patient variable be in scope from the application's knowledge of the patient context).
NOTE: Some of the FHIRPath content may need to be escaped (percent-encoded) in order to constitute a valid URL.
Aside from specifying a FHIR search string, the query can also be used to invoke operations. For example:
Observation/$stats?subject=Patient/123&code=2339-0&system=http://loinc.org&duration=24&statistic=average
would return an Observation resource with the average for Glucose [Mass/volume] in Blood (2339-0) in the last 24 hours for the specified patient.
This specification provides the following rules for the application/x-fhir-query
language: