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5.16Reading Data

 

This section contains information about methods for reading data from the CDR.

5.16.1Diff Operation

 

The $diff operation can be used to generate a differential between two versions of a resource, or even two different resources of the same type.

Differentials generated by this operation are in FHIR Patch format.

In generated differentials, where a value has changed (i.e. a replace operation), an additional part value will be present on the given operation called previousValue. This part shows the value as it was in the from version of the resource.

5.16.2Diff Instance

 

When the $diff operation is invoked at the instance level (meaning it is invoked on a specific resource ID), it will compare two versions of the given resource.

Parameters

  • fromVersion=[versionId]: (optional) If specified, compare using this version as the source. If not specified, the immediately previous version will be compared.
  • includeMeta=true: (optional) If specified, changes to Resource.meta will be included in the diff. This element is omitted by default.

To invoke:

GET http://fhir.example.com/baseR4/Patient/123/$diff

The server will produce a response resembling the following:

{
  "resourceType": "Parameters",
  "parameter": [ {
    "name": "operation",
    "part": [ {
      "name": "type",
      "valueCode": "replace"
    }, {
      "name": "path",
      "valueString": "Patient.name.family"
    }, {
      "name": "previousValue",
      "valueId": "Smyth"
    }, {
      "name": "value",
      "valueId": "SmithB"
    } ]
  } ]
}

5.16.3Diff Type

 

When the $diff operation is invoked at the type level (meaning it is invoked on a resource type but not on an individual instance), it will compare two different resources of the same type.

Parameters

  • from=[reference]: Specifies the source of the comparison. The value must include a resource type and a resource ID, and can optionally include a version, e.g. Patient/123 or Patient/123/_history/2.
  • to=[reference]: Specifies the target of the comparison. The value must include a resource type and a resource ID, and can optionally include a version, e.g. Patient/123 or Patient/123/_history/2.
  • includeMeta=true: (optional) If specified, changes to Resource.meta will be included in the diff. This element is omitted by default.

To invoke:

GET http://fhir.example.com/baseR4/$diff?from=Patient/1&to=Patient/2

The server will produce a response resembling the following:

{
  "resourceType": "Parameters",
  "parameter": [ {
    "name": "operation",
    "part": [ {
      "name": "type",
      "valueCode": "replace"
    }, {
      "name": "path",
      "valueString": "Patient.id"
    }, {
      "name": "previousValue",
      "valueId": "1"
    }, {
      "name": "value",
      "valueId": "2"
    } ]
  } ]
}