Add `RootSettings`

[rijenkii]

After making a discussion, question, and not getting any answers, I assume the functionality I'm looking for is not implemented, so I am making a feature request.

---

I want to use a following model for my settings:

import pydantic

class Clustered(pydantic.BaseModel):
    is_clustered: typing.Literal[True]
    server_name: str


class NonClustered(pydantic.BaseModel):
    is_clustered: typing.Literal[False] = False

Settings = pydantic.RootModel[Clustered | NonClustered]

~~In pydantic v1 it was possible to do such a thing (I think)~~

EDIT: Nope it wasn't

root@b8ce1c649a1f:/# cat main.py 
import typing
import pydantic

class Clustered(pydantic.BaseModel):
    is_clustered: typing.Literal[True]
    server_name: str


class NonClustered(pydantic.BaseModel):
    is_clustered: typing.Literal[False] = False

class Settings(pydantic.BaseSettings):
    __root__: Clustered | NonClustered

print(Settings().dict())
root@b8ce1c649a1f:/# python main.py 
Traceback (most recent call last):
  File "//main.py", line 15, in <module>
    print(Settings().dict())
          ^^^^^^^^^^
  File "/usr/local/lib/python3.12/site-packages/pydantic/env_settings.py", line 40, in __init__
    super().__init__(
  File "/usr/local/lib/python3.12/site-packages/pydantic/main.py", line 341, in __init__
    raise validation_error
pydantic.error_wrappers.ValidationError: 1 validation error for Settings
__root__
  field required (type=value_error.missing

But in v2 __root__ was removed, and multiple inheritance does not work:

>>> class Settings(pydantic_settings.BaseSettings, pydantic.RootModel[NonClustered | Clustered]): pass
... 
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/local/lib/python3.12/site-packages/pydantic/_internal/_model_construction.py", line 117, in __new__
    cls: type[BaseModel] = super().__new__(mcs, cls_name, bases, namespace, **kwargs)  # type: ignore
                           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "<frozen abc>", line 106, in __new__
  File "/usr/local/lib/python3.12/site-packages/pydantic/root_model.py", line 50, in __init_subclass__
    raise PydanticUserError(
pydantic.errors.PydanticUserError: `RootModel` does not support setting `model_config['extra']`

---

What I assume needs to happen is RootSettings has to be added, so the following code can be written:

Settings = pydantic_settings.RootSettings[Clustered | NonClustered]

[hramezani]

Thanks @rijenkii for reporting this.

Yeah, it is not possible in pydantic-settings but I think it is not possible to fetch data from env variables with your provided example in v1:

class Settings(pydantic.BaseSettings):
    __root__: Clustered | NonClustered

Have you tried it in v1?

[rijenkii]

You are right, it is not possible. I thought I've tried that, but it seems I've messed up somewhere. I've edited the OP (and the stackoverflow question) and redacted the part about v1.

[pavelrib]

@hramezani Actually, what was possible in pydantic v1 (given the example above):

Settings = typing.Union[Clustered, NonClustered]
pydantic.parse_obj_as(Settings)

Now fails when is_clustered=False in env var (I assume that it disregards the union). Any way around this, if we want to upgrade to pydantic v2?

[hramezani]

@pavelrib Have you tried TypeAdapter

[pavelrib]

@hramezani Thanks for the heads up, but can you please give an example of the usage in that case? I've figured you meant probably:

Settings: TypeAdapter[typing.Union[Clustered, NonClustered]] = TypeAdapter(typing.Union[Clustered, NonClustered])

But what's the next step to evaluate Settings? All examples show validation with an actual object, but here the values should be implicitly read from env.

[pavelrib]

@hramezani Is there anything that I'm missing here?

[hramezani]

No, I think TypeAdapter is not good for this usecase

[pavelrib]

@hramezani Is there any plan to add it in the near future? I've tried playing with different definitions and parsing methods to no avail.

[hramezani]

@pavelrib I don't think that I can add it shortly. I hope some contributors work on this but this can be a complex feature