FHIR Search Operations

A search operation allows to fetch resources, filtering them by supplied parameters. The parameters are a series of name=[value] pairs. The syntax for Read and Search is described here.

Search parameters can be encoded in the URL in case of a search by GET method:

GET [base]/[type]?name=value&...{&_format=[mime-type]}}

POST  [base]/[type]/_search{?[parameters]{&_format=[mime-type]}}

The response to any search operation is always a list of resources in a Bundle or an Operation Outcome.

Supported global FHIR search parameters

The following parameters apply to all resources:

Supported search parameter types

Each search parameter is defined by a type that specifies how the search parameter behaves. These are the defined parameter types:

{{host}}/fhir/Observation?code-value-quantity=10000-10$ge5.4
turnts to
{{host}}/fhir/Observation?code-value-quantity=10000-10$ge5.4|http://unitsofmeasure.org|g

Support of special search parameter types

Support of modifiers/prefixes for number/date search parameter type

Support of modifiers/prefixes for string search parameter type

Support of modifiers/prefixes for token search parameter type

Support of modifiers/prefixes for reference search parameter type

Support of modifiers/prefixes for uri search parameter type

Dynamic search

Search in the Kodjin FHIR Server is dynamic. In order to enable search on some new parameter, the SearchParameter resource must be added via API. The Elasticsearch index should also be configured.

Including other resources in result

To include additional resources to searchset response _include and _revinclude parameters could be used.

The parameter _include should be used to add referenced resources by requested resource. For example, managingOrganization should be added to searchset response for a Patient.

The parameter _revinclude should be used to add resources that has as a reference requested resource. For example, Encounter should be added while searching a Patient.

Parameter values for both _include and _revinclude have three parts, separated by a : character:

1. The name of the source resource from which the join comes
2. The name of the search parameter which must be of type reference
3. (Optional) A specific of type of target resource (for when the search parameter refers to multiple possible target types)

https://demo.kodjin.com/fhir/Observation?_include=Observation:patient:Patient

https://demo.kodjin.com/fhir/Patient?_id=123&_revinclude=Observation:patient

Requests for [_include|_revinclude]=* (asterisk) are supported by Kodjin. * will include or revinclude all possible references for requested resource.

https://demo.kodjin.com/fhir/Observation?_id=123&_include=*

Pagination

Search in Kodjin supports two types of pagination:

• offset pagination (with skip or page parameters)
• cursor pagination

curl --location --request GET 'https://demo.kodjin.com/fhir/Coverage' \
--header 'Prefer: pagination=offset-skip'

curl --location --request GET 'https://demo.kodjin.com/fhir/Coverage' \
--header 'Prefer: pagination=offset-page'

curl --location --request GET 'https://demo.kodjin.com/fhir/Coverage?_count=3' \
--header 'Prefer: pagination=cursor'

There are some special custom SearchParameters that are used for pagination. They are returned by Kodjin in the link element of the searchset Bundle.

Handling errors

Kodjin will not return an error if a parameter refers to a non-existent resource, e.g. GET [base]/Observation?subject=101, where "101" does not exist, or to an unknown code, e.g. GET [base]/Observation?code=loinc|1234-1, where the LOINC code "1234-1" is not known to the server. The response will be an empty search bundle.

Kodjin will return an error if it receives parameters from the client that it does not recognize, or parameters it recognizes but does not support (either in general, or for a specific search).

By default, the Kodjin FHIR Server ignores unknown or unsupported parameters for the following reasons: various HTTP stacks and proxies may add parameters that aren't under the control of the client.

Clients can specify how the server should behave by using the prefer header: -Prefer: handling=strict: Client requests that the server return an error for any unknown or unsupported parameter -Prefer: handling=lenient: Client requests that the server ignore any unknown or unsupported parameter.

```
{
    "resourceType": "OperationOutcome",
    "issue": [
        {
            "severity": "error",
            "code": "not-found",
            "details": {
                "text": "Unknown query param: test"
            }
        }
    ]
}
```

```
{
            "severity": "warning",
            "code": "value",
            "expression": [
                "Patient.name[0].text"
            ],
            "details": {
                "text": "Search on strings greater than 8000 symbols is not supported"
            }
        }
```