Populating embedded models with environment variables works but throws error with env file

[robcxyz]

When embedding two BaseSettings, I am able to populate the models with an environment variable but not with an env file. I would have expected the two methods to be equivalent but they are not.

Example:

import os
from pydantic_settings import BaseSettings, SettingsConfigDict
from pydantic import Field, ValidationError


class Child(BaseSettings):
    foo: str | None = None
    model_config = SettingsConfigDict(
        env_prefix='parent_child_',
        case_sensitive=False,
    )


class Parent(BaseSettings):
    child: Child = Field(default_factory=Child)
    model_config = SettingsConfigDict(
        env_prefix='parent_',
        case_sensitive=False,
    )

# Instantiate normally
p = Parent()
assert p.child.foo is None

# Instantiate with env var
os.environ['PARENT_CHILD_FOO'] = 'bar'
p = Parent()
assert p.child.foo == 'bar'
os.environ.pop('PARENT_CHILD_FOO')

# Instantiate with env file
env_file_contents = """
PARENT_CHILD_FOO=baz
"""
env_file_name = 'new_env_file'
with open(env_file_name, 'w') as f:
    f.write(env_file_contents)
try:
    p = Parent(_env_file=env_file_name)
except ValidationError as e:
    print(e)
    print('This should be valid given the environment variable was able to validate.')

os.remove(env_file_name)

Yields

1 validation error for Parent
child_foo
  Extra inputs are not permitted [type=extra_forbidden, input_value='baz', input_type=str]
    For further information visit https://errors.pydantic.dev/2.4/v/extra_forbidden
This should be valid given the environment variable was able to validate.

[hramezani]

Thanks @robcxyz for reporting this issue 🙏

There are couple of problem to fix:

1- As you can see in the docs, sub model has to inherit from pydantic.BaseModel

2- You need to specify env_nested_delimiter config

I've updated your provided example with the changes:

import os
from pydantic_settings import BaseSettings, SettingsConfigDict
from pydantic import BaseModel, Field, ValidationError


class Child(BaseModel):  # change
    foo: str | None = None


class Parent(BaseSettings):
    child: Child = Field(default_factory=Child)
    model_config = SettingsConfigDict(
        env_prefix='parent_',
        case_sensitive=False,
        env_nested_delimiter='__',  # change
    )

# Instantiate normally
p = Parent()
assert p.child.foo is None

# Instantiate with env var
os.environ['PARENT_CHILD__FOO'] = 'bar'  # change
p = Parent()
assert p.child.foo == 'bar'
os.environ.pop('PARENT_CHILD__FOO')  # change

# Instantiate with env file
env_file_contents = """
PARENT_CHILD__FOO=baz  # change
"""
env_file_name = 'new_env_file'
with open(env_file_name, 'w') as f:
    f.write(env_file_contents)
try:
    p = Parent(_env_file=env_file_name)
    assert p.child.foo == 'baz'  # change
except ValidationError as e:
    print(e)
    print('This should be valid given the environment variable was able to validate.')

os.remove(env_file_name)

[robcxyz]

@hramezani - Thank you so much for your response. This is exactly what I was looking for. Closing issue. Thanks again.