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3.2.5 FHIRPath Patch

FHIR Infrastructure Work Group

Maturity Level: 2

Standards Status: Trial Use

This page defines a FHIR Parameters-based, syntax-agnostic patch mechanism where elements to be manipulated by the patch interaction are described using their FHIRpath names and navigation.

3.2.5.1 Operations

This table documents the FHIR Patch operations that may be used to specify changes to a resource:

There are a few base rules that apply for all operations:

• The FHIRPath statement must return a single element
• The FHIRPath statement SHALL NOT cross resources using the resolve() function (e.g. like Observation.subject.resolve().identifier). resolve() SHALL only be used to refer to contained resource within the resource being patched. Servers SHALL NOT allow patch operations to alter other resources than the nominated target, and SHOULD return an error if the patch operation tries
• The type of the value must be correct for the place at which it will be added/inserted. Servers SHALL return an error if the type is wrong
• Servers SHALL return an error if the outcome of the patch operation is a not a valid resource
• Except for the delete operation, it is an error if no element matches the specified path
• Operations are applied in order, with each operation applied to the result of the previous patch operation

3.2.5.2 Parameters Format

The FHIRPath patch operations are encoded in a Parameters resource as follows:

• Each operation is a Parameter named "operation"
• Each operation has a series of parts, using the following parameter names from the table above with these types:

Here is an example of adding an element:

<Parameters xmlns="http://hl7.org/fhir">
  <parameter>
    <name value="operation"/>
    <part>
      <name value="type"/>
      <valueCode value="add"/>
    </part>
    <part>
      <name value="path"/>
      <valueString value="Patient"/>
    </part>
    <part>
      <name value="name"/>
      <valueString value="birthDate"/>
    </part>
    <part>
      <name value="value"/>
      <valueDate value="1930-01-01"/>
    </part>
  </parameter>
</Parameters>

3.2.5.2.1 Anonymous Types

Only some named datatypes (see the list) are allowed to be used directly in parameters. In order to add or insert other kinds of types - including anonymous elements (e.g. Observation.component, Timing.repeat), the content is defined by defining the name as described above, and instead of providing a value, a set of parts that are values are provided. Here is an example:

<Parameters xmlns="http://hl7.org/fhir">
  <parameter>
    <name value="operation"/>
    <part>
      <name value="type"/>
      <valueCode value="add"/>
    </part>
    <part>
      <name value="path"/>
      <valueString value="Patient"/>
    </part>
    <part>
      <name value="name"/>
      <valueString value="contact"/>
    </part>
    <part>
      <name value="value"/>
      <part>
        <name value="name"/>
        <valueHumanName>
          <text value="a name"/>
        </valueHumanName>
      </part>
    </part>
  </parameter>
</Parameters>

This pattern repeats as deep as necessary.

3.2.5.3 Choice Elements

Note that for elements with a choice of data types, the FHIRPath name in the name of the parameter does not include the data type suffix (per the rules in the FHIRPath Specification), but the parameter value does. Here's an example:

{
  "resourceType": "Parameters",
  "parameter": [{
    "name": "operation",
    "part": [{
      "name": "type",
      "valueCode": "add"
    }, {
      "name": "path",
      "valueString": "Specimen"
    }, {
      "name": "name",
      "valueString": "processing"
    }, {
        "name": "value",
        "part": [{
                "name": "description",
                "valueString": "testProcessing"
            }, {
                "name": "time",
                "valueDateTime": "2021-08-18T11:32:55.6462761+02:00"
            }]
            }]
    }
  ]
}

3.2.5.4 Extension Example

An example of adding an extension:

  <Parameters xmlns="http://hl7.org/fhir">
  <parameter>
      <name value="operation"/>
      <part>
        <name value="type"/>
        <valueString value="add"/>
      </part>
      <part>
        <name value="path"/>
        <valueString value="Specimen"/>
      </part>
      <part>
        <name value="name"/>
        <valueString value="processing"/>
      </part>
      <part>
        <name value="value" />
        <part>
          <name value="description" />
          <valueString value="test" />
        </part>
        <part>
          <name value="time" />
          <valueDateTime value="2021-08-13T07:44:38.342+00:00" />
        </part>
        <part>
          <name value="extension" />
          <part>
            <name value="url" />
            <valueUri value="http://example.org/fhir/DeviceExtension" />
          </part>
          <part>
            <name value="value" />
            <valueReference>
              <reference reference="Device/1">
            </valueReference>
          </part>
        </part>
      </part>
  </parameter>
</Parameters>

Applied to an empty Specimen, this would produce:

  <Specimen xmlns="http://hl7.org/fhir">
  <status value="available"/>
  <processing>
    <extension url="http://example.org/fhir/DeviceExtension">
      <valueReference>
        <reference reference="Device/1">
      </valueReference>
    </extension>
    <description value="test"/>
    <timeDateTime value="2021-08-13T07:44:38.342+00:00"/>
  </processing>
</Specimen>

There is a set of test cases for implementers in the fhir-test-cases repository.