Validators for optional dataclass fields are called twice

[bochecha]

Bug

Please complete:

• OS: Ubuntu 19.04 and Fedora 30
• Python version import sys; print(sys.version): 3.7.3 and 3.7.4
• Pydantic version import pydantic; print(pydantic.VERSION): 0.32.2

The following code snippet is a simplified version of my code, to illustrate the problem:

from typing import Optional

from pydantic.class_validators import validator
from pydantic.dataclasses import dataclass


@dataclass
class Dataclass:
    field1: int
    field2: Optional[int] = None

    @validator('field1', pre=True)
    def get_field1(cls, value: int) -> int:
        print(f'get_field1({value})')

        if not isinstance(value, int):
            raise ValueError(f'{value} is not an int')

        return value

    @validator('field2', pre=True)
    def get_field2(cls, value: Optional[int]) -> Optional[int]:
        print(f'get_field2({value})')

        if not isinstance(value, int):
            raise ValueError(f'{value} is not an int')

        return value


Dataclass(field1="foo", field2="bar")

Running it gives the following:

get_field1(foo)
get_field2(bar)
get_field2(bar)
Traceback (most recent call last):
  File "reproducer.py", line 31, in <module>
    Dataclass(field1="foo", field2="bar")
  File "<string>", line 4, in __init__
  File "pydantic/dataclasses.py", line 75, in pydantic.dataclasses._process_class._pydantic_post_init
    # __delattr__
  File "pydantic/main.py", line 785, in pydantic.main.validate_model
pydantic.error_wrappers.ValidationError: 3 validation errors for Dataclass
field1
  foo is not an int (type=value_error)
field2
  bar is not an int (type=value_error)
field2
  bar is not an int (type=value_error)

As you can see the get_field2 validator is called twice. This happens whenever the field is Optional.

This results in 2 identical errors being shown, which is very confusing.

[samuelcolvin]

This is a duplicate of #737, but it should also be fixed in v1 which will be released soon.

The best solution for now is to use whole=True in the validator.

[bochecha]

This is a duplicate of #737, but it should also be fixed in v1 which will be released soon.

The best solution for now is to use whole=True in the validator.

Thanks, I'm using whole=True for now.

I see you've released 1.0 in the meantime, is that now fixed? (#737 was already closed when you marked this as a duplicate so it's hard to tell)