property: Optional[ComplexObject] = field(None, nullable=True) doesn't create a nullable field in openapi spec

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Example

Here’s a self-contained, minimal, reproducible, example with my use case:

import enum

from typing import Optional

import pytest

from fastapi import FastAPI
from pydantic import BaseModel, Field


app = FastAPI()


class RHELVersions(enum.Enum):
    """Available RHEL versions within the database."""

    el7: str = "RHEL 7"
    el8: str = "RHEL 8"
    el9: str = "RHEL 9"


class DeviceEntry(BaseModel):
    """A model which represents the single hardware device."""

    simple_property: Optional[bool] = Field(None, nullable=True)
    complex_property: Optional[RHELVersions] = Field(None, nullable=True)


@app.get("/", response_model=DeviceEntry)
def read_root() -> DeviceEntry:
    return DeviceEntry(simple_property=None, complex_property=None)


def test_case():
    spec = app.openapi()
    assert spec["components"]["schemas"]["DeviceEntry"]["properties"][
        "simple_property"
    ]["nullable"]
    with pytest.raises(KeyError):
        assert spec["components"]["schemas"]["DeviceEntry"]["properties"][
            "complex_property"
        ]["nullable"]


"""
  +  'components': {'schemas': {'DeviceEntry': {'description': 'A model which '
  +                                                            'represents the '
  +                                                            'single hardware '
  +                                                            'device.',
  +                                             'properties': {'complex_property': {'$ref': '#/components/schemas/RHELVersions'},
  +                                                            'simple_property': {'nullable': True,
  +                                                                                'title': 'Simple '
  +                                                                                         'Property',
  +                                                                                'type': 'boolean'}},
  +                                             'title': 'DeviceEntry',
  +                                             'type': 'object'},
"""

Description

Run pytest {path_tothe_module}. Simple property has nullable in the apispec, but complex property doesn’t.

Environment

• OS: [e.g. Linux / Windows / macOS]: Linux
• FastAPI Version [e.g. 0.3.0]: 0.62

To know the FastAPI version use:

python -c "import fastapi; print(fastapi.__version__)"

• Python version: 3.9

To know the Python version use:

python --version

Additional context

[Mause]

See the following example:

import enum

from typing import Optional

from pydantic import BaseModel


class RHELVersions(enum.Enum):
    """Available RHEL versions within the database."""

    el7: str = "RHEL 7"
    el8: str = "RHEL 8"
    el9: str = "RHEL 9"


class DeviceEntry(BaseModel):
    """A model which represents the single hardware device."""

    simple_property1: Optional[bool]
    complex_property1: Optional[RHELVersions]
    simple_property2: bool
    complex_property2: RHELVersions


assert DeviceEntry.schema() == {
    'definitions': {
        'RHELVersions': {
            'description': 'Available RHEL versions ' 'within the database.',
            'enum': ['RHEL 7', 'RHEL 8', 'RHEL 9'],
            'title': 'RHELVersions',
        }
    },
    'description': 'A model which represents the single hardware device.',
    'properties': {
        'complex_property1': {'$ref': '#/definitions/RHELVersions'},
        'complex_property2': {'$ref': '#/definitions/RHELVersions'},
        'simple_property1': {'title': 'Simple Property1', 'type': 'boolean'},
        'simple_property2': {'title': 'Simple Property2', 'type': 'boolean'},
    },
    'required': ['simple_property2', 'complex_property2'],
    'title': 'DeviceEntry',
    'type': 'object',
}

Note the required field - this how you mark whether a field is optional or not

[tiangolo]

Thanks for the help here @Mause ! 👏 🙇

Thanks for reporting back and closing the issue @ZhukovGreen 👍