FastAPI OpenAPI spec of an endpoint using Pandera not working with Pydantic v2

[airibarne]

FastAPI OpenAPI spec of an endpoint using Pandera not working with Pydantic v2

[cosmicBboy]

Hi @airibarne can you report what the failure is exactly?

[airibarne]

Sure @cosmicBboy, thanks for the quick response. Here is a screenshot of the error:

It seems to be a schema generation issue, but I am not familiarized enough with the way Pandera integrates with Pydantic to expose its JSON schema to fully assess it.

I'd add, for extra context, that this is breaking the /docs page of a standard FastAPI application having an endpoint that uses a Pandera model as either an input or an output. The only workaround I found up to today is to exclude these endpoints from the final OpenAPI schema using FastAPI's include_in_schema (documented here).

[cosmicBboy]

The part of the code base responsible for converting pandera schema to json schema representation can be found here:

pandera/pandera/api/pandas/model.py

Lines 574 to 604 in cf6b5e4

	if PYDANTIC_V2:
	@classmethod
	def __get_pydantic_core_schema__(
	cls, _source_type: Any, _handler: GetCoreSchemaHandler
	) -> core_schema.CoreSchema:
	return core_schema.no_info_plain_validator_function(
	cls.pydantic_validate,
	)
	@classmethod
	def __get_pydantic_json_schema__(
	cls,
	_core_schema: core_schema.CoreSchema,
	_handler: GetJsonSchemaHandler,
	):
	"""Update pydantic field schema."""
	json_schema = _handler(_core_schema)
	json_schema = _handler.resolve_ref_schema(json_schema)
	json_schema.update(_to_json_schema(cls.to_schema()))
	else:
	@classmethod
	def __modify_schema__(cls, field_schema):
	"""Update pydantic field schema."""
	field_schema.update(_to_json_schema(cls.to_schema()))
	@classmethod
	def __get_validators__(cls):
	yield cls.pydantic_validate

For simplicity it only converts pandera schemas to a very simple json schema representation (column names and types).

Feel free to make a PR for this!