Cannot use a custom pydantic-aware class with FastAPI query Depends()

test_comma_separated_query_strings.py

from enum import Enum
from typing import Optional, Generic, TypeVar, Set

from fastapi import FastAPI, Depends
from pydantic import BaseModel
from pydantic.fields import ModelField

ContainerType = TypeVar('ContainerType')


class Color(str, Enum):
    """Cat colors."""

    RED = 'red'
    WHITE = 'white'
    BLACK = 'black'


class CommaSeparated(Generic[ContainerType]):
    """Comma separated values of a container."""

    @classmethod
    def __get_validators__(cls):
        """Ensure pydantic compatibility."""
        yield cls.validate

    @classmethod
    def validate(cls, raw_value: str, field: ModelField) -> ContainerType:
        """Validate the raw value."""
        raise ValueError(
            'I will write this validation later, too lazy right now :(',
        )


class CatsQuery(BaseModel):
    """Query our cats herd."""

    color__in: Optional[CommaSeparated[Set[Color]]] = None


app = FastAPI()


@app.get('/cats')
def list_cats(query: CatsQuery = Depends()):
    """Filter the herd of cats and list them."""


app.openapi()

'''
Error:

    get_openapi_operation_request_body
        body_schema, _, _ = field_schema(
    ../venv/lib/python3.8/site-packages/pydantic/schema.py:222: in field_schema
        f_schema, f_definitions, f_nested_models = field_type_schema(
    ../venv/lib/python3.8/site-packages/pydantic/schema.py:475: in field_type_schema
        assert field.shape == SHAPE_SINGLETON, field.shape
    E   AssertionError: 10
'''