How to deal with openapi_core.casting.schemas.exceptions.CastError: Failed to cast value to object error

[chris-young-12-nhs]

Hi,

I'm using openapi-core to validate responses against this OpenAPI schema:

https://digital.nhs.uk/restapi/oas/573240

The error I'm getting is this:

    def _cast_proparties(self, value: Any, schema_only: bool = False) -> Any:
        if not isinstance(value, dict):
>           raise CastError(value, self.schema["type"])
E           openapi_core.casting.schemas.exceptions.CastError: Failed to cast value to object type: b'\n    \n        \n        \n        {"entry":[{"fullUrl":"https://internal-dev.api.service.nhs.uk/validated-relationships/FHIR/R4/RelatedPerson/47CD795E","resource":{"id":"47CD795E","identifier":[{"system":"https://fhir.nhs.uk/Id/nhs-number","value":"9730675929"}],"patient":{"identifier":{"system":"https://fhir.nhs.uk/Id/nhs-number","value":"9730676399"},"type":"Patient"},"relationship":[{"coding":[{"code":"MTH","display":"mother","system":"http://terminology.hl7.org/CodeSystem/v3-RoleCode"}]}],"resourceType":"RelatedPerson"},"search":{"mode":"match"}}],"link":[{"relation":"self","url":"https://internal-dev.api.service.nhs.uk/validated-relationships-service-api/FHIR/R4/RelatedPerson?identifier=9730675929&patient%3Aidentifier=9730676399"}],"timestamp":"2024-04-23T17:01:35+00:00","total":1,"type":"searchset","resourceType":"Bundle"}\n'

../../../../../Library/Caches/pypoetry/virtualenvs/tests-puqZLLMN-py3.9/lib/python3.9/site-packages/openapi_core/casting/schemas/casters.py:114: CastError

The call I am making that raises this error is:

    openapi_response = RequestsOpenAPIResponse(api_response)
    openapi_request = RequestsOpenAPIRequest(api_response.request)
    openapi.validate_response(openapi_request, openapi_response)

Where api_response is a requests.models.Response:

(Pdb) type(api_response)
<class 'requests.models.Response'>
(Pdb) api_response.content
b'\n    \n        \n        \n        {"entry":[{"fullUrl":"https://internal-dev.api.service.nhs.uk/validated-relationships/FHIR/R4/RelatedPerson/47CD795E","resource":{"id":"47CD795E","identifier":[{"system":"https://fhir.nhs.uk/Id/nhs-number","value":"9730675929"}],"patient":{"identifier":{"system":"https://fhir.nhs.uk/Id/nhs-number","value":"9730676399"},"type":"Patient"},"relationship":[{"coding":[{"code":"MTH","display":"mother","system":"http://terminology.hl7.org/CodeSystem/v3-RoleCode"}]}],"resourceType":"RelatedPerson"},"search":{"mode":"match"}}],"link":[{"relation":"self","url":"https://internal-dev.api.service.nhs.uk/validated-relationships-service-api/FHIR/R4/RelatedPerson?identifier=9730675929&patient%3Aidentifier=9730676399"}],"timestamp":"2024-04-24T10:05:26+00:00","total":1,"type":"searchset","resourceType":"Bundle"}\n'

So it looks like openapi-core is expecting a dict but is getting bytes:

openapi-core/openapi_core/casting/schemas/casters.py

Lines 113 to 114 in 99af2d3

	if not isinstance(value, dict):
	raise CastError(value, self.schema["type"])

(Pdb) openapi_response.data
b'\n    \n        \n        \n        {"entry":[{"fullUrl":"https://internal-dev.api.service.nhs.uk/validated-relationships/FHIR/R4/RelatedPerson/47CD795E","resource":{"id":"47CD795E","identifier":[{"system":"https://fhir.nhs.uk/Id/nhs-number","value":"9730675929"}],"patient":{"identifier":{"system":"https://fhir.nhs.uk/Id/nhs-number","value":"9730676399"},"type":"Patient"},"relationship":[{"coding":[{"code":"MTH","display":"mother","system":"http://terminology.hl7.org/CodeSystem/v3-RoleCode"}]}],"resourceType":"RelatedPerson"},"search":{"mode":"match"}}],"link":[{"relation":"self","url":"https://internal-dev.api.service.nhs.uk/validated-relationships-service-api/FHIR/R4/RelatedPerson?identifier=9730675929&patient%3Aidentifier=9730676399"}],"timestamp":"2024-04-24T10:15:31+00:00","total":1,"type":"searchset","resourceType":"Bundle"}\n'
(Pdb) type(openapi_response.data)
<class 'bytes'>

I have worked round this by subclassing RequestsOpenAPIResponse so the data attribute returns a dict which works for me but I'd like to understand why I'm seeing this issue in the first place and what, if anything, I am doing wrong.

Thanks

[p1c2u]

Hi @chris-young-12-nhs

Probably you don't have registered proper deserializer. What schema and content-type are defined for the response in your spec?

[chris-young-12-nhs]

Thanks @p1c2u.

The content-type is application/fhir+json The customer has mandated this as the content-type
fhir is Fast Healthcare Interoperability Resources - https://www.hl7.org/fhir/overview.html

The schema is the one I liked to in the OP - https://digital.nhs.uk/restapi/oas/573240.

Do I need to create a deserializer for application/fhir+json like the one in the example here:

https://openapi-core.readthedocs.io/en/latest/customizations/extra_media_type_deserializers.html

And make it return a dict?

Thanks for your help.

[p1c2u]

Exactly that; you can use the same function as standard one

from openapi_core.deserializing.media_types.util import json_loads

[chris-young-12-nhs]

That's great @p1c2u thanks's o much