Using CQL with FHIR
1.0.0 - STU1 International flag

This page is part of the Using CQL with FHIR Implementation Guide (v1.0.0: STU1) based on FHIR (HL7® FHIR® Standard) R4. This is the current published version. For a full list of available versions, see the Directory of published versions

Operations

Index

CodeSystemDescription
CQL CQL

The $cql operation evaluates a CQL expression and returns the result. The operation has a single return parameter that can be of any type to accommodate the possible result types of a CQL expression.

CQL Library Evaluate

Evaluates the contents of a library and returns the results as a Parameters resource.

Examples

$cql

Simple Expression

This example just evaluates the expression 2 + 2:

POST [base]/$cql

{
  "resourceType": "Parameters",
  "parameter": [{
    "name": "expression",
    "valueString": "2 + 2"
  }]
}

The expected response for this operation is:

HTTP/1.1 200 OK

{
  "resourceType": "Parameters",
  "parameter": [{
    "name": "return",
    "valueInteger": 4
  }]
}
Expression With Parameters

This examples evaluates the expression 2 + X where X is a parameter passed in the parameters parameter with the value of 2:

POST [base]/$cql

{
  "resourceType": "Parameters",
  "parameter": [{
    "name": "expression",
    "valueString": "2 + X"
  }, {
    "name": "parameters",
    "resource": {
      "resourceType": "Parameters",
      "parameter": [{
        "name": "X",
        "valueInteger": 2
      }]
    }
  }]
}

The expected response for this operation is:

HTTP/1.1 200 OK

{
  "resourceType": "Parameters",
  "parameter": [{
    "name": "return",
    "valueInteger": 4
  }]
}
Expression Referencing a Library

This example evaluates the expression Count(PE."Blood Glucose Observations"), where "Blood Glucose Observations" is defined in the ParameterExample library and made available to the expression through the library parameter:

POST [base]/$cql

{
  "resourceType": "Parameters",
  "parameter": [{
    "name": "expression",
    "valueString": "Count(PE.\"Blood Glucose Observations\")",
  }, {
    "name": "subject",
    "valueString": "Patient/example"
  }, {
    "name": "parameters",
    "resource": {
      "resourceType": "Parameters",
      "parameter": [{
        "name": "GlucoseThreshold",
        "valueQuantity": {
          "value": 8.0
          "code": "mg/dL",
          "system": "http://unitsofmeasure.org"
        }
      }]
    }
  }, {
    "name": "library",
    "part": [{
      "name": "url",
      "valueCanonical": "http://hl7.org/fhir/uv/cql/Library/ParameterExample"
    }, {
      "name": "name",
      "valueString": "PE"
    }]
  }]
}

The expected response for this operation is (assuming a Patient with id example and 4 Blood Glucose Observations over 8.0 ‘mg/dL’):

HTTP/1.1 200 OK

{
  "resourceType": "Parameters",
  "parameter": [{
    "name": "return",
    "valueInteger": 4
  }]
}

NOTE: The parameter name may be qualified by the identifier used for the library to explicitly indicate that the parameter value should only be bound to the parameter in that library, for example:

  }, {
    "name": "parameters",
    "resource": {
      "resourceType": "Parameters",
      "parameter": [{
        "name": "PE.GlucoseThreshold",
        "valueQuantity": {
          "value": 8.0
          "code": "mg/dL",
          "system": "http://unitsofmeasure.org"
        }
      }]
    }
  }, {

The local identifier PE is specified by the library.name part.

Library/$evaluate

This example evaluates the ParameterExample library

POST [base]/Library/ParameterExample/$evaluate

{
  "resourceType": "Parameters",
  "parameter": [{
    "name": "subject",
    "valueString": "Patient/example"
  }, {
    "name": "parameters",
    "resource": {
      "resourceType": "Parameters",
      "parameter": [{
        "name": "GlucoseThreshold",
        "valueQuantity": {
          "value": 8.0
          "code": "mg/dL",
          "system": "http://unitsofmeasure.org"
        }
      }]
    }
  }]
}

The expected response for this operation is (assuming a Patient with id example and 4 Blood Glucose Observations over 8.0 ‘mg/dL’):

HTTP/1.1 200 OK

{
  "resourceType": "Parameters",
  "parameter": [{
    "name": "Blood Glucose Observations",
    "resource": {
      "resourceType": "Observation",
      "id": "observation-1",
      ...
    }
  }, {
    "name": "Blood Glucose Observations",
    "resource": {
      "resourceType": "Observation",
      "id": "observation-2",
      ...
    }
  }, {
    "name": "Blood Glucose Observations",
    "resource": {
      "resourceType": "Observation",
      "id": "observation-3",
      ...
    }
  }, {
    "name": "Blood Glucose Observations",
    "resource": {
      "resourceType": "Observation",
      "id": "observation-4",
      ...
    }
  }]
}

NOTE: The parameter name may be qualified by the library name to explicitly indicate that the parameter value should only be bound to the parameter in that library, for example:

  }, {
    "name": "parameters",
    "resource": {
      "resourceType": "Parameters",
      "parameter": [{
        "name": "ParameterExample.GlucoseThreshold",
        "valueQuantity": {
          "value": 8.0
          "code": "mg/dL",
          "system": "http://unitsofmeasure.org"
        }
      }]
    }
  }, {