Reference search :identifier modifier

[Erik Brakke]

From the conformance statement:

• The token search modifier :of-type and the reference search modifier :identifier aren't supported.

Is the :identifier modifier on the roadmap?

Thanks!

-Erik

[Paul Church]

There hasn't been enough demand for this to get it onto the roadmap so far - I don't think identifier references have achieved widespread use.

There is a partial workaround through custom search parameters, as pointing a token search parameter's fhirpath expression to [reference field].identifier will index the system/value and act like an identifier search, e.g. ?my-identifier-reference-search=system|value - but because this is not a reference search, related functionality like chaining and include will not work.

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[Erik Brakke]

Thank you Paul for the insights and the workaround!  Looking forward to custom search going GA.

[Maico Bernal]

Hello there,

Is the :of-type modifier on the roadmap? 

Do you know any workaround solution using custom search parameters for that purpose?

What i need is a way to search for a identifier value of a specific type. 

I have tried with multiples expressions like Person.identifier.where(type.coding.code = value) or .identifier.where(type.coding.where(code = '1')) with this parameters i list below but i get a error 400 with INVALID_ARGUMENT and no more clues about whats wrong.

"code": "dni",

"base": ["Person"],

"type": "token",

"status": "active",

"expression": "Person.identifier.where(type.coding.where(code = '1'))",

"xpathUsage": "normal"

"error": { "code": 400, "message": "failed to parse search parameter PersonNationalIdentifierSearch", "status": "INVALID_ARGUMENT" }

Any help or suggestions will be appreciated.

[Erik Brakke]

If your identifier system aligns with the type, searching on system might be an option.

Person?identifier={system}|{value}

The {value} after the pipe is optional

Person?identifier={system}|

Will return all resources of that identifier system.  And, behind the scenes it is an indexed search, so it performs well.

-Erik

[Paul Church]

The issue with the expression you're trying is that custom search parameter expressions don't support "where()" clauses (except in the specific case of extension URLs, since that is a common pattern). The limitations should hopefully be clear from https://cloud.google.com/healthcare-api/docs/how-tos/fhir-custom-search#expression

Emulating the exact functionality of :of-type with custom searches is not quite possible. You can define an expression that walks into that sub-field, e.g. Person.identifier.type (a CodeableConcept so as a token parameter it will support system|value, or pointing the expression to Person.identifier.type.coding.code is an option if you only care about the code), and then search by Person?my-identifier-type-param=[system|value] but this doesn't combine with the value of the identifier the way of-type does.

If you did a search for Person?identifier=[value]&my-identifier-type-param=[system|value], this risks unintended matches if an individual resource has multiple identifiers, one of which matches identifier=[value] while another matches my-identifier-type-param=[system|value]. If you can constrain the assumptions of the use case so that doesn't happen, this may still be viable as a workaround.

Alternately, as Erik points out there are a fair number of use cases where the identifier system aligns with the type so searching by system is sufficient.

Support for :of-type is not currently on the roadmap. It is being tracked but has not come up often as a priority for customers.

To view this discussion on the web visit https://groups.google.com/d/msgid/gcp-healthcare-discuss/f4f31484-68eb-4aba-a387-f3d37341be9dn%40googlegroups.com.

[Maico Bernal]

Thank you both for the responses.

Your explanation about the expression limitations is very clear. I understand now that there's no direct workaround since custom search parameters don't support where() clauses (totally missed that line on the docs)

Our specific case involves a client that sends identifiers with a unique system but three different types of identifier. While the probability of collisions (same identifier.value for different type.coding.codes) is low, we tested the suggested approach of Person?identifier=[value]&my-identifier-type-param=[system|value] and encountered the exact issue you described - the FHIR store returns matches when an identifier.value exists in one identifier entry but the type matches in a different identifier entry of the same resource.

As a workaround, we'll implement post-processing using FHIRPath in our application layer to validate that Person.identifier.where(type.coding.where(code = '1')) matches the specific identifier.value we're searching for.

Thanks for explaining the current status regarding :of-type support and your helpful suggestions.

Best regards,
Maico