Optional field with validate_default only performs one field validation

[reritom]

Initial Checks

• I confirm that I'm using Pydantic V2

Description

When validating a class that has field_validators for optional fields that have validate_default=True, only one error gets returned based on the first field_validator. None of the basic validation errors get returned (like missing), and no sequential field_validators get called.

Given a model with optional fields with default values, validation of defaults, and field validators:

class ExampleKO(BaseModel):
    value_0: str
    value_a: Annotated[Optional[str], Field(None, validate_default=True)]
    value_b: Annotated[Optional[str], Field(None, validate_default=True)]

    @field_validator("value_a", mode="after")
    def value_a_validator(cls, value):
        raise AssertionError

    @field_validator("value_b", mode="after")
    def value_b_validator(cls, value):
        raise AssertionError

When called with no arguments we only get 1 validation error. The first field_validator.

ExampleKO()

"""
pydantic_core._pydantic_core.ValidationError: 1 validation error for ExampleKO
value_a
  Assertion failed,  [type=assertion_error, input_value=None, input_type=NoneType]
    For further information visit https://errors.pydantic.dev/2.4/v/assertion_error
"""

I would expect the above to behave the same as if I passed two None values for those optional fields:

ExampleKO(value_a=None, value_b=None)

"""
value_0
  Field required [type=missing, input_value={'value_a': None, 'value_b': None}, input_type=dict]
    For further information visit https://errors.pydantic.dev/2.4/v/missing
value_a
  Assertion failed,  [type=assertion_error, input_value=None, input_type=NoneType]
    For further information visit https://errors.pydantic.dev/2.4/v/assertion_error
value_b
  Assertion failed,  [type=assertion_error, input_value=None, input_type=NoneType]
    For further information visit https://errors.pydantic.dev/2.4/v/assertion_error
"""

Example Code

from typing import Annotated, Optional

from pydantic import BaseModel, Field, field_validator

class ExampleKO(BaseModel):
    value_0: str
    value_a: Annotated[Optional[str], Field(None, validate_default=True)]
    value_b: Annotated[Optional[str], Field(None, validate_default=True)]

    @field_validator("value_a", mode="after")
    def value_a_validator(cls, value):
        raise AssertionError

    @field_validator("value_b", mode="after")
    def value_b_validator(cls, value):
        raise AssertionError


ExampleKO()

"""
pydantic_core._pydantic_core.ValidationError: 1 validation error for V2ExampleKO
value_a
  Assertion failed,  [type=assertion_error, input_value=None, input_type=NoneType]
    For further information visit https://errors.pydantic.dev/2.4/v/assertion_error
"""

Python, Pydantic & OS Version

pydantic version: 2.4.2
        pydantic-core version: 2.10.1
          pydantic-core build: profile=release pgo=false
                 install path: /Users/me/Documents/Projects/pydanticbug/.venv2/lib/python3.9/site-packages/pydantic
               python version: 3.9.12 (v3.9.12:b28265d7e6, Mar 23 2022, 18:22:40)  [Clang 13.0.0 (clang-1300.0.29.30)]
                     platform: macOS-13.5-arm64-arm-64bit
             related packages: typing_extensions-4.8.0

[sydney-runkle]

Hi @reritom,

Thanks for reporting this. This is a bug in our validation error handling in pydantic-core, and we're working on a fix. Stay tuned 👍.

[reritom]

@sydney-runkle is there an issue on pydantic-core that I can follow? I didn't see one regarding this when I checked. Thanks

[sydney-runkle]

Hi @reritom,

We don't have an issue there - your filing of this issue alerted us to this bug. I'll have a PR up shortly in both pydantic-core and pydantic working on this fix.

Thanks again for bringing this issue to our attention 😄