Fastapi: Calling root_validator on pydantic body input yields dictionary type

[moldhouse]

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Example

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

from fastapi import FastAPI
from pydantic import BaseModel, root_validator
from typing import Optional, Dict, Any

app = FastAPI()

class UserUpdate(BaseModel):
    password: Optional[str]
    name: Optional[str]

    @root_validator
    def validate(cls, values: Dict[str, Any]) -> Dict[str, Any]:
        return values

@app.patch("/me", response_model=schemas.User)
def update_user_me(
    user_in: UserUpdate,
) -> Any:
    assert isinstance(user_in, dict)
    return user_in

Description

• Using root_validator in the pydantic model changes the behavior of the dependency injection, instead of return an instance of UserUpdate, a dict is returned
• Commenting out the root_validator in the pydantic model leads to the expected behavior, in this case user_in is an instance of UserUpdate
• I would expect user_in to be of type UserUpdate

Environment

• OS: [e.g. Linux / Windows / macOS]: Linux

• FastAPI Version [e.g. 0.3.0]: 0.61.1

• Python version: 3.8.5

[David-Lor]

You should rename your "def validate" to something else (like "def _validate"). "validate" is an existing method for pydantic's BaseModel, so you are overriding it with yours, causing that unexpected behaviour. I tried it and after renaming the root_validator function name, it works as expected.