# FastAPI Pydantic

{{tag>FastAPI Pydantic openapi}}

## PydanticObjectId

<code python>
from datetime import datetime
from pydantic import BaseModel
from bson.objectid import ObjectId


class PydanticObjectId(ObjectId):
    @classmethod
    def __get_validators__(cls):
        yield cls.validate

    @classmethod
    def validate(cls, v):
        if not isinstance(v, ObjectId):
            raise TypeError('ObjectId required')
        return str(v)
        
class ModelBase(BaseModel):
    id: PydanticObjectId = Field(None, alias='_id')
</code>

이렇게 하면 사용할 수 있으나, [[OpenAPI]] 사용시 에러 발생

## str 타입으로 사용

<code python>
class ModelBase(BaseModel):
    id: str = None
</code>